I have a friend who has had a mastodon instance since it was gnu social, and there are two reasons I stopped using it.
First, the UI sucks. He installed 3 or 4 different skins and they were all barely usable. I don't want or need something flashy, xfce is my favorite windows manager, but it needs to at least work and not be confusing.
Second, the people suck. It went from being okay to by the time I left I don't think I was seeing any exchanges that didn't have antisemitism or racism.