You wouldn't be rolling your own crypto? You could use standard crypto but with your own app/UI to make the crypto easy to use.
And why would "your own" app be easier to use than somebody else's?
I didn't mean "your own" app would be easier to use, I meant the crypto would be easier to use via an app instead of using it through the command line.
Then you have to worry about security from side channel attacks. Even things like the iOS or Android task-switcher UI caching screenshots of your app can be vectors.
Oh yeah, making an app that is easy to use and still secure is definitely not easy. But at least you would know how you implemented the encryption on it.
If you don't write your own source code and write your own compiler/interpreter to run it you're doing it wrong. Oh, and let's not forget firmware.