Ive been using the official and deprecated android client for a long while now, and haven’t experienced any problems
is there really any need to switch to syncthing-fork at the moment?
I’ve used 4+ devices, with untrusted intermediaries, and big syncthing folders 
As long as the app works and syncs, it should do the job. Just be aware that you likely won’t receive any support if you encounter issues (either with the app, or with the underlying Syncthing version, which is still on the v1 channel). Outdated software is also more likely to have security-related vulnerabilities.
To be honest, in our setup, we also still operate one device running the old Android app with no plans to upgrade or switch to anything else (at least in the foreseeable future), simply because there is no alternative that I can vouch for in terms of reliability and stability. This is also for someone, who isn’t very tech-savvy, so running Syncthing via Termux, etc. (which I personally do) isn’t a solution in that case.