I agree with you that if one wants to quickly shift from one investment to another it is much easier if the two investments are held at the same institution. However, it is no more difficult to trade TBIL than it is to trade T-Bill CUSIP 912796CS6 (maturing Sept 28) at a brokerage.
It's apples and oranges to discuss "buy[ing] CD/treasuries direct" after starting with "Looking at treasuries at Schwab with a maturity of 9/15 to 9/30".
You would not buy CD/treasuries direct. How about MMFs? Would you buy a MMF direct from the fund family (e.g. IDSXX from Columbia Threadneedle)?
It looks like the ease and flexibility you're describing is something associated with the institution (brokerage) rather than the type of security being traded.

I changed CG=100K + coverted $25K from T-IRA to taxable for each person = $150K income..and the numbers for Fed+State tax stayed the same.
Again, even if I was 60 years old and not living in GA, I would not buy CD/treasuries direct. MM or ETF=TBIL for treasuries allow me a much easier and more flexible way. It's especially easier with big numbers.
Most household retirees have small portfolios, about $400K. Most don't need income beyond 80-100K (including SS)

Notary & Signature Guarantee
Notaries just require state registrations/licenses to operate. Some get it for earning extra income on the side. Many currency exchanges have notaries. Many legal offices have someone on staff as notary. All a notary is vouching is that the signature belongs to the one signing it (in front of them) - there is no liability beyond that (and any liability would be the loss of registration/license).
Signature Guarantee is same as Medallion Signature Guarantee. It is by bank or financial institution officer. Beyond authentication of signature, there is also financial liability about the soundness of the document being guaranteed. In some Signature Guarantees at my local bank, I have gone through almost half-hour interview process on what/why I am doing something. Once for a 529 signature guarantee, the guy thought something looked strange, and he called the 529 program right away to determine if what I was doing was allowed by them. Good that I had prior related correspondence from the 529.
It's a long way of saying that I doubt some kid at the local FedEx or UPS store can do Signature Guarantee.

Yesterday I stopped by Fidelity to drop off a $30 check. I told the rep to put the money into my premium MMF, not the core fund. Fidelity usually executes this correctly. But when I got home, I looked at the receipt and saw that it went into "Core".

What a tragedy!
Have you calculated your before tax loss on this error by Fidelity over the next 12 months? FSOA - let’s assume perhaps the “Core” account is yielding 4.75% and the “Premium” 5% … On a $30 deposit it appears you’re receiving about a penny a month less in interest than what you’d have earned had Fidelity not screwed up.
Brings to mind BF - “A penny saved …” :)

I want to own funds+MM that I can trade any day when I see an opportunity.
Treasuries are just as liquid as funds. Though convenience can be subjective.
You can see below that each one of us got a $65K Retirement Income Exclusion.
Actually from what you posted I can't see that you're not being taxed on marginal SCOXX income (well, the non-Treasury part of it anway). That's because you put in just a $1 placeholder for your conversions. If you're really converting more than $7100, then each marginal dollar of SCOXX income got taxed at 5.75% x (1 - 18.2%) as I described previously.
If this exclusion works for you, great. That doesn't mean it works for most people.
In the end, this exclusion applies to a sliver of a sliver of a sliver of taxapayers. As stated in the piece you cited, they are those taxpayers who are (i) lower income (ii) retiree households (iii) in Georgia.
https://www.kiplinger.com/retirement/602202/taxes-in-retirement-how-all-50-states-tax-retirees

a married couple filing jointly may exclude twice the given limit.
This makes it sound as if a couple gets a combined exclusion that's double the individual exclusion. That's not quite accurate.

The exclusion is available for the taxpayer and his/her spouse; however, each must qualify on a separate basis.

From instructions for GA state income tax Schedule 1 subtractions.
https://dor.georgia.gov/document/document/2022-it-511-individual-income-tax-booklet/download
More importantly, the Feb 3, 2023 report puts this tax break in perspective by identifying the taxpayers targeted for this benefit:"PUBLIC BENEFIT  The exclusion provides relief to lower-income retiree households..."
No matter. There are lots of people who don't benefit from this break - because they're not lower income, or because they're not over age 62 (retired or not), or maybe they don't live in Georgia all the time if at all.
Even if the difference is 0.2-0.4% annually why bother?
Good question. Why bother making a point of such a small difference?

Looking at treasuries at Schwab with a maturity of 9/15 to 9/30 and I see YTM of 4.09 to 5.066. I will stick with my Schwab Treasury Obligations Money Fund – Ultra Shares (SCOXX) that pay "only" 5.2%

The idea is to make meaningfully more money and not concentrate on 0.2-0.4% more per year. I just don't like the inconvenience of CD and treasuries. I want to own funds+MM that I can trade any day when I see an opportunity. Several days of investing in my bond mutual funds on one trade can make much more than 0.4%. If I wanted to use treasuries I may consider something like TBIL where it's easier to trade.
I used my real tax software. I entered $140K as capital gains, no other income(just kept $1 for SS and $1 for conversion since I want to keep these entries), and both of our ages 65.
You can see below that each one of us got a $65K Retirement Income Exclusion.
When I entered $140K capital gains, Fed taxes came at $15,720...GA taxes=0. Basically, $140K FEDERAL ADJUSTED GROSS INCOME (AGI) = $10K GEORGIA ADJUSTED GROSS INCOME (AGI)
When I entered $150K capital gains, Fed taxes came at $17,920...GA taxes=$48. Basically, $150K FEDERAL ADJUSTED GROSS INCOME (AGI) = $20K GEORGIA ADJUSTED GROSS INCOME (AGI).
Looking at big numbers shows that it's a sweet deal, most retirees filing jointly with age greater than 65 wouldn't pay GA taxes on income close to $150K.

Way back when biotech had really hot streaks, CELG grew so much that it paid for a wedding and still occupied way more than 5% of our Schwab account. Then biotech cooled off and BMY bought the company and screwed the shareholders out of some rights we had earned. Some &%@#ers in green eye shades did their jobs on us.

"So, you will start out with an edge of 63 +12.5 = 75.5 bps with FRN." Isn't it where you end that counts ? @yogibearbull I'm seeing red on the T-Notes, but once rates start to fall, that is hopefully they do, then the red should start to reverse. When I'm talking red, that is shown in Schwab account, so think that is the difference if I had rolled 1 month T-Bills. YBB any thoughts on that last statement ?
Thanks , Derf

Compare 2-yr T-Note (regular) to 2-yr FRN:
2-yr T-Note (regular) 4.92% (fixed; 8/18/23)
2-yr FRN 3-mo T-Bill yield (5.55%, 8/18/23, but will vary weekly) + spread (around +12.5 bps at 8/23/23 Auction).
So, you will start out with an edge of 63 +12.5 = 75.5 bps with FRN.

I have a 2 & 3 year T-note in account , 3.75% & 4.25% rate. I may have started to early purchasing longer maturities , so will someone tell when to go longer. HA HA !! Next purchase will be another 2 year followed by a 3 year T-Note. I don't want to be late when the light turns green.
Rolling longer, Derf

a married couple filing jointly may exclude twice the given limit.
This makes it sound as if a couple gets a combined exclusion that's double the individual exclusion. That's not quite accurate.

The exclusion is available for the taxpayer and his/her spouse; however, each must qualify on a separate basis.

From instructions for GA state income tax Schedule 1 subtractions.
https://dor.georgia.gov/document/document/2022-it-511-individual-income-tax-booklet/download
More importantly, the Feb 3, 2023 report puts this tax break in perspective by identifying the taxpayers targeted for this benefit:"PUBLIC BENEFIT  The exclusion provides relief to lower-income retiree households..."
No matter. There are lots of people who don't benefit from this break - because they're not lower income, or because they're not over age 62 (retired or not), or maybe they don't live in Georgia all the time if at all.
Even if the difference is 0.2-0.4% annually why bother?
Good question. Why bother making a point of such a small difference?

Looking at treasuries at Schwab with a maturity of 9/15 to 9/30 and I see YTM of 4.09 to 5.066. I will stick with my Schwab Treasury Obligations Money Fund – Ultra Shares (SCOXX) that pay "only" 5.2%

I've a feeling I'm the big outlier here...66% of my investments are in 1 stock. Though my portfolio is for sure unlike any here....15% wine & spirits, 10% cattle, around 1% mutual funds, and the rest rental real estate.

Still growing my single-stocks. Biggest holdings are right now at 4.84% and 4.1% of my overall total. I could certainly see putting maybe 8% or higher of my total in those two. Good dividend payers, solid track record. I'm holding a total of 5 stocks. Gonna get rid of one particular loser after the week-end. 4 to 5 stocks might be a sweet-spot for me. KISS the thing.

I invest mostly in mutual funds and ETFs but do own one individual stock.
I prefer to limit individual stocks to ≤ 5% of my total portfolio.
This offers protection against potentially large losses from overly concentrated positions.
Extremely concentrated equity positions were a significant factor
in achieving wealth for some of the richest people on earth.
With that said, I don't expect to join the billionaire's club but hope to achieve more moderate financial success.

Most funds can be bought directly with a $2.5k minimum. Some as low as $1k. For simplicity, I chose TRP brokerage--- because my T-IRA was already there. But TRP won't let you invest in someone else's mutual fund unless you come up with a $5k minimum. That's double of what the fund house demands. Stinky-poopy.
I'm pretty much always fully invested. I don't wanna take $5k from Peter to give to Paul, just in order to start a mutual fund position. I don't make many changes within the T-IRA. I use the brokerage for single stocks.
The T-IRA is no longer being added to. I am deliberately growing the stuff in the brokerage account. Until I started with single stocks, I found it easy to deal with the different fund houses. There were never very many. DoubleLine, TRP, Mairs & Power.

(https://www.audits2.ga.gov/reports/summaries/retirement-income-exclusion/)
Published: February 3, 2023.. QUOTE: "In 1981, Georgia enacted an income tax exclusion for retirement income received by taxpayers aged 62 years and over. Currently, taxpayers aged 65 and over may exclude up to $65,000, while those 62 to 64 (as well as those permanently and totally disabled) may exclude up to $35,000. The exclusion applies to retirement income such as capital gains, interest, and pensions, as well as up to $4,000 of earned income. Limits apply to individual taxpayers, so a married couple filing jointly may exclude twice the given limit. The exclusion is intended to induce retirees to live in Georgia and provide a boost to economic growth."
=================
Even if the difference is 0.2-0.4% annually why bother? I look for an easy way to trade without any hurdles. MM is a great holding place until the next trade and when I'm in, I invest at 99+%.
Most of our money is in IRAs (Roth+Rollover) anyway.

"Cutting losses quickly and letting profits run" is the right way.
1) It took me about 18 years (1995-2013) to get it until I got to a nice-size portfolio. In those years I was invested at 99+%. When the funds I owned lagged, I just switched to better-performing risk/reward funds.
2) In 2013, I added 2 new rules based on quicker market movements. Sell any stock/allocation fund if it loses more than 6% from the last top and sell any bond fund with more than 3% loss.
3) In 2017, one year prior to retirement, I implemented a new system, trading mostly bond funds. I would sell any bond fund before it reaches a 1% loss from the last top. Trading in/out is based on the big picture(risk is very high=out, otherwise=in) + uptrends.
Basically, I could be 99+% in or out. It's not about relative performance anymore, it's about protecting my portfolio first.

Last year, SCOXX / SNOXX was only 18.8% state tax exempt (and 0% exempt in Calif., N.Y., and Conn.)
https://www.schwabassetmanagement.com/resource/2022-supplementary-tax-information.
Even in Georgia, with its 5.75% state income tax, after you chop off 5.75% x 5.2% x (1 - 18.8%) or 0.24% for state tax, one is left with less than a 5% return. Own Treasuries and the full yield is state tax exempt.

Good question @Ben. However, what’s more desirable for one person might be less desirable for another.
I held funds at as many as 5 different houses at one time. Perfectly workable. Over very long time horizons there was a reluctance to depend on any single fiduciary firm, advisor or money manager - not knowing how they might change or be affected by things beyond their control some day. However, when you’re down to your last 10-20 years of life and when the probable time to shift 100% into cash is 10 years away or less, than the advantage noted of spreading the money around among 4 or 5 different mutual fund fudiciaries houses ceases to be much of a factor. (Ie : I don’t expect T.Rowe Price or American Funds to go “belly-up” any time in the next 10 years.) Of course, it’s somewhat of an empty argument anyway because even if the firm failed, money inside a fund is supposed to be perfectly safe.
One thing having money at 5 different houses did was allow me to move in and out of different sectors pretty much at will. I began spreading my money around after the SEC got involved big-time is seeing that funds prohibit “excessive trading” around 2000 (following some very real abuses). ISTM they went overboard. So, for instance, if I wanted to sell some of my REIT, gold or natural resource holdings only two weeks after increasing the position at one fiduciary, I could lighten up at a different where I held a similar fund without running amuck of anyone’s rules. With ETFs now available and the ability to own / trade stocks or CEFs through a full service broker pretty much at will, that concern has faded. Now (for me, anyway) it’s mutual funds for the really large, dominant long-term positions and ETFs or CEFs for the areas I’m apt to trade.
But, hey - if it works for you don’t change it.
@msf said: ”A minor plus of buying directly is the ability to do Roth conversions (within a single family) by dollar amount rather than in number of shares as brokerages require.”
Nice reminder … I did a “quickie” conversion of 100% of holdings at D&C and Oakmark in early March ‘09. Phoned each on a Friday afternoon as markets plummeted. They explained everything and emailed links to the necessary documents the same day. Got the paperwork into USPS overnight mail Monday morning. Wasn’t a lot of time to be terribly fussy about what to convert, if anyone remembers what the beginning of March 2009 was like.
@Ben - One big advantage of staying with the various houses is ability to trade without worrying about “early redemption” fees (in most cases anyway). With NTF funds at Fido anything sold within 60 days incurs a fee, and with some brokerages it’s 90 days. Also, fund to fund exchanges are a bit faster at a house. Only by about 1 extra day, however, based on my experience with Fido.

When you get to a certain asset level, larger fund houses may give perks. T Rowe Price will let you into its closed funds (like PRWCX) if you maintain $250K there. And at $500K, they will sell you cheaper institutional class shares (e.g. TRAIX) at "just" a $50K min.
At Vanguard, you can buy Admiral class shares that most brokerages don't sell. And at the Flagship level ($1M in Vanguard funds) you get 25 free trades per year of other family funds. That's really a brokerage perk layered on top of buying Vanguard funds directly.
Then there's BRUFX, not available at brokerages at any price.
A minor plus of buying directly is the ability to do Roth conversions (within a single family) by dollar amount rather than in number of shares as brokerages require. Direct ownership of a bond fund often comes with the ability to write checks directly against the fund (though tax implications of that can be messy).
Brokerages often waive loads (NTF) or give you access to lower ER institutional class shares with lower mins (TRP and Vanguard aside). They make bookkeeping a bit easier (single 1099, all assets in one place). They often have better cash management services (bill pay and such).
Regarding executor work - been there, done that. I was certainly capable. It was nevertheless a chore to deal with more institutions, getting more letters testamentary, doing several mailings. It's not so much a matter of feasibility as it is of ease.
My personal preference is to use brokerages (as few as possible) for convenience and access to I class shares. But to buy funds with limited access or to buy cheaper share classes I'll deal directly with the fund house if necessary.