$5 was just for the lifetime ad free version. Sync Ultra was more expensive because it had more features, like being able to see deleted comments (there are more but I don't remember them)

$5 for the 8 years I used Sync for Reddit is cheap as fuck looking back. $20 is totally fair if I use this app even half as long.

The only "ads" I see are an occasional black box that says "sponsored content".