I agree that $20USD for ad-free is a bit high, but on the other hand I used Sync for Reddit for roughly 10 years and paid $2.50 at the time.
So I consider it a way to give back for the great experience I had in the past.
And we got used for mobile apps being dirt-cheap, but most of us don't have any issue paying even more for sitting in a dirty movie theater for a 2½ hours movie with a popcorn and soft drink.
Yep - I bought sync way back in the day and paid less than $5 for it. Used it for years and years across multiple devices until I switched to iOS. I got my moneys worth for sure - $20 seems like a bargain.