I came here to find out the same thing, just skimming around I think the differences are mainly 2 things:
1. Renpy version isn't caught up yet, it was started earlier but then it looks like everything went to the RPGM version?
2. RPGM version looks like it's a more complete experience, the Renpy version is more streamlined?
That's the impression I got, I'll be going for the RPGM version. And it still blows my mind that people use phones (instead of PC) to play these kind of games. The new modern era is incredible.