People are upset because they want to use a premium service without paying for it. The dev was kind enough to add a free version, which is supported by ads. However, the ads in the free version use trackers (just like pretty much every ad service), so people are getting hysterical that the app is "spying" on them.
It would be one thing if this was the only app for Lemmy, but there's numerous other apps on the market they could use.
Although none of them are even half as polished as Sync 😉
Full-size keyboard or bust.