@Andreas-PÖLZL But apps installed could crash both apps, and cause bad syncs, and also can cause a bricked watch. That was often discussed here.
I am on iOS but Android is the same I thing.
You can use both apps and the watch. But always be sure that only ONE app is running, even in the back. I use MC to sync my watch to Movescount and Strava, then close the app, wait a couple of minutes to be sure no process is running in the background. Then start the SuuntoApp and sync again. And close the app when sync is finished. Works for months now. Sometimes I forget the close MC or SA in the back while opening the app, and then it just doesn’t work, and sometimes it forces the watch to start new.