[mrslave]

Agreed. When I'm selling Nix to other Linux users, instead of getting lost in an explanation of deterministic package versions, I tell them system upgrades are atomic: you either enter the new environment or you don't. Either way you're in a consistent state. If for some reason there's difficulty booting, you can always go back to the previous system state from the boot menu. Mostly Debian and Gentoo users have nibbled on this bait. Arch users less so. YMMV

[neil-mayhew]

It's even better than reverting the whole system because you can still run an executable from the old system in the new system. Once, I found out that video had stopped working for me in Zoom but because I hadn't used it in a while there had been multiple system updates since then. I was able to bisect through the previous system profiles and find the most recent version that still had working video. I used this for a month or so until the bug was fixed in the current version.

[SuperSandro2000]

I always forget to explain that. Atomic updates are one of the best if not the best feature of nixos.