I'm not gonna tell you not to go for it. However, the reason most of the other apps connect to bank accounts is because that way they can actually get the whole picture information that's needed to make them useful. How are you going to get the transactions without connecting to their bank account? Have them enter the transactions? I'm going to forget, and I might have far too many to do by hand. I'll enter 3, mistype one, and then give up.

Also, the easiest way to monetize is for it to be paid. You did hard work; why shouldn't you be paid for it?