I love how your reply (which mentions that you use NixOS) is at the top because it indirectly confirms my experience with Nix. I tried Nix on Debian only a couple of weeks ago, and the main issue I had with Nix was that whenever I searched for an answer or other info relating to Nix, most of what I found was written by users of NixOS, not standalone Nix. It seemed that the overwhelming majority of people sharing info about Nix are users of NixOS.

For example, notice how there are 4-5 times as many results when searching the web for "configuration.nix" (which is used with NixOS) than there are when searching for "config.nix" (which is used with standalone Nix):

https://www.google.com/search?q=%22configuration.nix%22

https://www.google.com/search?q=%22config.nix%22

I got bored of wading through irrelevant search results, so I uninstalled Nix. (My experience with Guix was even worse, but in a different way.) When I want software that isn't in Debian's repos, I'll stick to installing it from source like I've been doing forever.