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.