It uses OSTree to manage state, and only allows mutability inside of the home directory and /var.
Overall I was very impressed. Another year or two of rounding out the typical use cases and it will make a fine immutable workstation.
It uses btrfs instead of OSTree. It only allows writes inside /home, /var, /tmp, /etc, ... and everything else is updated transactionally.
Configuration of my system is mostly easy when setting up (dnf install xyz, plus 2 config file tweaks in /etc). It's the config of everything in /home that's complex (gnome settings, my emacs, bash and git config etc.).
It's a trade-off. I like it because I want a system that always works and updates silently, and I don't make heavy customizations. It's probably not for you.