This comment from the Twitter thread by @filmore sums it up for me:
I haven’t tried Mastodon, but the feeling I get from the descriptions I’m seeing on the web is that it seems like it would be good for people who think Linux will take over the PC market. Doing stuff like having to pick a home-grown server to join, worrying about which servers have questionable content, having to just know how to search for stuff, and things like that make it seem more geared to the techie who doesn’t mind dealing with all the computing muck. It may scoop up a lot of tech-savvy and hardcore Twitter users, but it doesn’t sound like something that the general public would enjoy using. People who just want to scroll through comments as a way to pass time will probably go to something which is tailored to a more casual experience.
I had trouble figuring out how to make Twitter work. I’ve had a couple of accounts and have abandoned them because I couldn’t figure them out. No way I’m going to try Mastodon.