In my experience you can have:

1. Good app that is free with ads,
2. Good app that is paid without ads,
3. Shit to mediocre app that is free without ads.

I’ve tried many alternatives, but so far the intuitiveness and beautiful UX of Sync stand apart from the competition for me. I respect FOSS apps, and even prefer them in some cases. But let’s not pretend that its the best approach for every developer, or that anyone who releases a non-FOSS app is automatically greedy or sketchy.