Isn't nix mostly for multi-system install?
I did the nix thing a few years ago, spent a month on the config, and then never needed it again. Personally, I don't see a use-case for single desktop installation ;)
I use multiple systems and even I feel NixOS is overkill, especially with their confusing and sometimes incomplete documentation.
On the other hand, Nix the package manager has been fantastic - especially if you're on an immutable OS, or running some ancient "stable" distro - you can get all the packages you want, without breaking your system - and no need to learn the Nix language and write convoluted config files.
I'm running nix on my PC turned server, and there's definitely a lot of advantages...I highly recommend it for people who can pick up languages easily and prefer fixing a problem once by brute force trial and error.
Doing easy things is much harder, but doing hard things can be laughably easy
I probably wouldn't pick it as-is for my primary PC, but for a server? Amazing.