I honestly don't see what the problem is. If you prefer FOSS use FOSS apps.
I've tried every single Lemmy app for iOS and Android, but I can honestly say nothing comes close to how smooth and native Sync feels.
I wasn't even a Sync user on Reddit so I didn't understand the hype, but I get it now. On my Pixel 6 Pro all of the other Lemmy apps had some kind of issues, whether that be random crashes or frame rate issues. But Sync is just so smooth and feature rich.
I've also joined the sync discord and the developer is very clear on what type of data he collects (He doesn't, but Google may).
Also with the pricing, if you don't agree with the price that's your opinion, but the amount of complaining is ridiculous. He made the app so whatever he wants to charge is his decision. You can also still freely use the app (with ads) so no one is forcing you to buy.