I was considering using My Savings Direct today, because of the 4.35% APR. But I found out the personal/taxable Vanguard brokerage account is setup with Federal Money Market by default with a current yield of 4.4% APR. So I just opened up a brokerage account with them. (There is no $20 annual fee since I am doing digital only communications.) [I already had a Solo Roth 401K with vanguard; after signing up for the personal/taxable brokerage account with them, it now shows both accounts on my account overview screen, using the same login -- convenient.]
I trust Vanguard more and I can simply do an ACH transfer each month to Vanguard and that's it.. it compounds monthly. I don't even have to buy a fund or etf, as the default cash account is mm. It's also nice that I can directly buy some VTI from this account as well when needed. They told me it only takes 3 days to ACH transfer back the money to my bank, when needed.. that's liquid enough for me.
I am also no longer going to bother with the treasury bills from treasury direct (due to overhead of waiting for auction date, the delay between auction date and issue date, lack of liquidity, delay in ach transfers back and forth, the manual reinvesting etc.).. I will just transfer the extra money from my bank each month to this vanguard account -- it pays about the same.. probably better since it compounds monthly and not as much delay.