My wife and I run an onlyfans account, a manyvids account and a few other related accounts. I can tell you from extensive networking with other onlyfans creators the number of them using chatters is pretty small, probably less than 1%. I personally have never interacted with someone that uses them. I also run a discord and telegram support server for creators so I interact with a lot, but certainly have not made any kind of scientific measure.
Some higher tier models use agencies to run their stuff and that's usually where the chatters come into play.
The general consensus is to avoid agencies or managers for obvious reasons.
While I personally think it's kind of shady, I very much doubt it's illegal, but ianal. There is one fans platform that I know of that has integrated AI chat bots so shrug