Oh, I-Bonds are totally better yield than T-Bills and more tax efficient than money markets.. no question about that.
However, when adjusting for the hassle/time of dealing with the TD website, for me at least, isn't worth it. I'd rather have everything consolidated at Fidelity. It'll also make it easier on my spouse to manage, if I happen to meet and untimely demise.
It really depends on your timeframe. With the inverted yield curve of T bills right now, 3-4 months seems to be the peak yields at around 5.2%. You obviously can't sell I bonds for a year so it's not really comparable. The 52 week T bill is less appealing at ~4.6%. But if you sell your I bonds at 1 year, you lose the last 3 months of interest, so that'd be an effective rate of ~4.4%. The 52 week T bill still wins and is probably easier to deal with and has more flexibility since it can actually be sold before the year is up if you buy at a brokerage.
VUSXX (Vanguard Treasury Money Market) is 4.68% right now. It's generally been state tax exempt, but it looks like it's only around 60% exempt right now. So not as good tax-wise. And the rate is not locked in which could be good or bad. But there's also a benefit in that it's more liquid if you needed it tomorrow.
So if I was looking at strictly a 1 year investment right now, I'd skip I bonds personally. I'd do VUSXX or a similar fund and roll 3-4 month T bills. That's basically what I'm doing for my short-term cash right now, although my timeframe may be less than a year as well. Not guaranteed to beat I bonds or a 52 week T bill. But you have some added flexibility and higher short-term yields right now. If rates keep going up, this is definitely the better way to go. If rates start dropping, locking in longer terms probably would've been better. Who knows. That's why I don't think I bonds are quite a slam dunk for your shorter-term EF anymore, but could still work for that if desired and certainly wouldn't be a bad decision.
I don't find TreasuryDirect to be that bad. I've never had to jump through any hoops and even changed my bank account without issue (it seems they somewhat recently improved this). I just don't log in and check it very often. But it doesn't matter because it just sits there collecting interest. Not much I need to do other than buy once a year if I desire. People seem to really hate TD. Yeah it's old and clunky, but it works for me. If you needed to deal with the BS getting a signature, then I understand the frustration but that's hopefully a one-time thing. Once you have the account and can log in, I don't see why keeping it open is a very big deal. But I can understand wanting to simplify to a single brokerage and I'm a fan of Fidelity as well.