It's free. It's only on google play. The 20$ is to get rid of ads forever. There's also a subscription model which I'm not a fan of but it only costs 17$/year.
I'm a sync user and I love sync because of the customisation and the UI. It was pretty much my perfect reddit app.
Pepsi, Coke, or Budget no-name cola?
Windows, MacOS, or Linux?
Sometimes it's a personal preference.
I like the UX of Sync. I've made QOL feature requests in the past and they've been implemented. For an early beta, it's extremely well polished. I can afford to support the developer for a quality app, so I do.
I can certainly see the merits of each app, and have used a few of them.
I just prefer Sync.
But that's me. It should have no bearing on what you or anyone else uses.
People act like they're being forced to use Sync when there are decent alternatives. Sync just happens to currently have the best layout/user interface with tons of customisation.
Whether or not that's worth paying money for is up to each individual but I can't stand the constant complaining. Either deal with ads or don't use it if you don't like it 👍