On top of what other already said they accidentally DDOS'd the Aur repos and took it down for couple hours one time.
Looks like they do add quite a bit security features. Having SELinux installed and working out of the box being the biggest. https://fedoraproject.org/wiki/Security_Features
Yeah! of course when I say a small instance, I don't mean a random instance with 10 users. You should check it out before you join. There is a lot of great instances with ~1000 users. Maybe should add it to the post.