If you have $3000 rent due, you can keep $3000 in checking to pay that, but you should not put that money in the stock market, since it could be worth only $2700 at the due date. Therefore I think the statement "We offer a checking account alternative that lets users invest their balance (not FDIC insured), otherwise it works just like a normal checking account" invites trouble. People should use checking accounts primarily to pay bills, so risky investments do not belong in them.