I'm all on board with FOSS, but I used sync for reddit for years, ljdawson has my support on Lemmy too. I don't mind supporting a good dev. Do I prefer things be FOSS? Yeah, but I have no issues using a closed source product if it works. And sync has always been top notch. Responsive dev, all around good product.
The dev is also in England where the cost of living is skyrocketing. For me $20/yr for a staple app on my phone that's constantly being updated is totally reasonable.