This sounds like a total nightmare. I am very interested in Nix and was strongly considering setting it up on my new travel laptop as a daily driver but stories like these give me pause. I would love to get a more detailed explanation of what happened here. Either way I am past the phase where I'm comfortable or patient enough to beta test software so Debian / Ubuntu it is for me.
Nix daily driver for years here. I don't know what they did to screw up their system like that, but it's unusual IME. Normally you can just reboot and load the previous profile. Even in the absolute worst case, as long as you have your config, you could boot the installer and then load your config and your system comes back exactly as it was. It's definitely not beta software.
FWIW, I used Debian more than anything over decades, and also have little patience when it comes to unstable computers. NixOS is a breath of fresh air and has reinvigorated my love of Linux. I haven't found it less stable than Debian, and also have a higher degree of confidence when making changes. It has its quirks, but ultimately I've found it a joy to use, and I'm never going back to a distro that doesn't have similar capabilities.
If you boot default Debian and apt install a handful of packages from the primary channel, it probably doesn't matter much, but if you enjoy even a modest amount of customizing, NixOS really shines. From one Linux user to another, I encourage you to try it! I have no affiliation, just an old head stoked on Nix.
I used nix years ago on a Mac just as a sort of alternative to what I’d otherwise use homebrew for and I really liked it, so I decided a few times that i would try nixos for my laptop. Each time I was stopped by the awful documentation and the weird “flakes are experimental but kinda required” state of the project and I gave up.
This year I decided to give it another try and set it up on an ancient laptop using Claude to factor the config and it’s gone so well that I now use the same nix config to manage three different machines and it’s insanely liberating to know how easy it is to screw everything up and roll it back trivially. I now regularly make edits on one machine and then just routinely commit them and go apply on the other machines with zero friction. It’s kind of amazing.