The IB Key app on android is convenient, but they could make it much better. It currently doesn't support finger-print recognition (at least not on my Nexus 6P), so I have to type a pin into it. The app also seems a bit slow/laggy for what it does. You'd think some app that only grabs a challenge phrase and verifies a pin could be very fast... But when opening the app, it takes a few seconds before it's ready.
Yes, the Android app is shitty. It's not a real, native Android app. They use WebViews, which are slow. The back button doesn't work etc.
I don't use it because while it IS easier to type a 4-digit PIN (the minimum length) than to look up the numbers on the physical card, I prefer the security of the card. (Though if someone with eidetic memory sees it, you're toast : )