Its not quite that simple. As I explained in a different thread the value add is not just backup its cloud sync. We already considered all of this earlier on in the design. While its conceptually possible to use external cloud storage it wouldn't give us the back end support we need. Drive, dropbox etc are simple cloud storage containers and don't have the rich API support we need.

I love subscriptions. They allow me to buy gear in incremental phases, but I don't subscribe to any real services that don't have a payoff at the end.
 
Momentum looks good, but not something I'd really use. I really like the visual design of the program.
 
The only Android app that I really use is Chord.
 
https://play.google.com/store/apps/details?id=com.rabugentom.chord&hl=en
 
You can punch in any series of notes for the guitar (or bass), and it will show you the key, scale, chord name, etc. If you want to convert guitar chords and scales to keyboard, it shows you that also. Supports extra strings and allows you to define alternate or dropped tunings. I have profiles for my six-string bass and 7-string guitar.