From memory there’s a fee in order to publish an app the the play store so I would assume they’re circumventing that by hosting the app on their own website. You could also upload the app to virustotal and see what that says if you are concerned.

I’m not a big video editing guy but I have used kdenlive in the past and was happy with it

Honestly if it wasn’t for sync I wouldn’t have used reddit nearly as much, It will be a shame to see it go