This looks really useful!
Its just what I've needed on a couple trips I've taken, where something smaller than a backpack but larger than a wallet is needed. And the stow-away fanny pack straps are really a good idea.
I think this would be good as an in-flight bag too. You could put a small water bottle, phone, paperback book, and headphones in there. I looks like it fits in the end pocket of an Aeronaut with room to spare.