Much more customizable and in my opinion far easier to navigate, and for some reason way cuter. You can also download the app right from Firefish when you sign up, there’s no dealing with the app store. I don’t quite know but it’s super friendly, all sorts of strangers greeted me and followed me when I joined, which definitely didn’t happen with Mastodon. I just find it strangely adorable and full of cool people and very positive, and for some reason I don’t find Mastodon that way.