There are lots of open questions and issues, or? Is there any better reason not to use nixos (for anything but a minimal server …)?
If someone tells you the nixos-rollback is a none experimental feature or even “bullet proof”, but it’s not. Don’t even think of changing the DM or Channel (e.g. to unstable and back) or live with the consequences e.g. of a broken system without any clue about the reason…