Yeah requiring travel to do it would make it prohibitive. But 3.5% for a 4 month cash investment is really really good these days.
And what does one do after 4 months?
I can't consider this passive income, as it actually requires time spent (going to a branch, meeting with a banker and openings an account - I did that today at a local bank just because I needed a safe deposit box, with no line and 0 travel time, it took at least 15 minutes to open a checking account).
And for an emergency fund - I personally prefer Paid-Up-Additions on a life insurance policy, the value grows by about 3%-4% per annum, fully liquid, no 1099-INT and a small added death benefit.