Also forgot to mention you don’t earn interest while your money is moving in ACH transfers. So if we assume 4 days(maybe low if you hit any weekends) for each transfer on a 1 month T bill: 4 days from your bank to broker, 4 days from broker back to your bank when TBill redeems, and then 4 days to River for a total of 12 days in transit. That means despite the 1 month TBill rate being around 4.6% currently, out of a 45 day period potentially 1/3 of that time you are earning no interest while your money is moving. So your effective rate on that TBill is much lower.
*this is highly dependent on your bank and broker and could be significantly different