FWIW, we only did fingerprint protection for opening the app on iOS because of community requests and still plan to do it on Android, again because of community requests 
If you asked most people here, we felt that locking your phone is the most important thing and we’ll protect making payments etc. of course, but having protection in the app to stop someone who happens to pick up your unlocked phone seeing your Monzo feed is overkill. But feedback from people here and in in-app chat convinced us otherwise