This seems to be the model I've witnessed with many apps over the years. Free at first to get traction and users, then ads, then pay one time fee to get rid of ads, then subscription to keep using the app.
Then there are those that wouldn't even pay a single fee and get upset at the thought as everything should be free.
The part that is upsetting is the contributions the early community made is monetized when they were ~~they~~ there for the benefit of the community.
I do see there are costs to maintaining and updating these apps so I can understand a need to keep revenue flowing for these future costs. The one time payment is a hell of a deal for years with updates to accommodate the revisions needed for each system update let alone functionality improvements.
In the old days we would buy software for our PC and that was it. There wasn't really any updates or further support for newer versions of Windows. The software would become very insecure or just stop functioning altogether with enough changes to windows.
It's hard to find the right balance. I know I only want to pay once, or heck never, but I want these upgrades and updates too.