> My only concern with it would be how sustainable it is in the long term.

Another concern should be: can you trust molly? Cryptographers have been auditing Signal... who is auditing molly?

In addition, it looks like third-party apps (there are a few) that interface with the official Signal client maybe against Signal's TOS. They haven't enforced it yet from what I can see but it's a possibility and that's a fairy large risk IMO.