I feel this is it but surely there are other apps following this model. I'm assuming they are probably the biggest but definitely not the only ones doing it. For good* ad-free software that is being actively developed and will get used probably every day for years, $100 seems more than fair to me. Beats paying a subscription indefinitely imo. I paid for the Plex lifetime pass for similar reasons and that was worth every penny.
*Good is subjective, just because you wouldn't pay doesn't mean others won't.

Edit: formatting