Nix

NixOS does not do snapshots of the complete system.

The "rollbacks" that are available built-in apply only to changes applied by the configuration.nix.

You can run NixOS on ZFS and get the best of both worlds.

This is nice because /nix is reproducible, so you can make a ZFS filesystem for /nix that you don't snapshot (or at least, don't retain old snapshots). Since so much lives in /nix, the rest of your root filesystem is pretty light, and you can snapshot that for easy backups.

For booting, selecting a NixOS configuration to boot is smoother than selecting a ZFS snapshot. Something like systemd-boot is preferable over something like ZFSBootMenu.