[SilasX]

Merely substituting one low-risk instrument for another doesn't seem like a meaningful difference in this context.

Coincidentally, just two days ago I commented on the distinction to someone suggesting this kind of service: https://news.ycombinator.com/item?id=35790913

[prottog]

There's one critical difference, which is that only chartered banks within the Federal Reserve system can take advantage of the federal funds rate, whereas anyone (including individuals) can buy T-bills.

The Fed, for various reasons, implicitly disallow this type of narrow bank. Several people have tried but the Fed always denied their application to join the system.

[SilasX]

Aren’t they basically the same rate?