I'm a longtime Ubuntu user and recently gave NixOS a try as most of our team use it. I have to admit I was highly skeptical as it all looks very complicated. The learning curve was a bit steep due to the documentation and odd terminology. But after you get going it solves so many problems. The fact you can declare you're entire desired set up in a single configuration.nix then "nixos-rebuild switch" and you're done saves so much time.
I tried to fully switch my work environment to NixOS 2 or 3 years ago. I really like the concept and I think it's a very good approach to reproducible build environments, in theory it's much cleaner than the massive data replication you get with e.g. Docker.
I only lasted for a month or two though, for a couple of reasons. The main one was that I had a lot of trouble with Python packages - Nix suggests a certain approach for dealing with them which didn't work very well for me and I didn't manage to set up an alternative that I liked. (For Haskell I loved working with Nix though!) A lot of software I use also wasn't available in the repositories and I tried to build some packages but found the Nix language a bit obtuse. The basic syntax and logic are not too hard but I still found many of the packages I used as examples very confusing.
In the end I'm back to Ubuntu using Docker whenever I need reproducible environments.
