I think the Nix language is a big barrier to entry for NixOS, I’ve used it quite a bit and still struggle to debug problems, I think lack of types or some basic type inference doesn’t help.

That said I’ve had a very positive experience packaging NodeJS apps with Nix, the /nix/store lends itself very nicely to the mess that is node_modules as each NPM package can be stored once in the store and NodeJS can read the dependencies directly from /nix/store if using something like Yarn PNP, I wrote a Yarn plugin to make this a bit easier https://github.com/madjam002/yarnpnp2nix Using Nix as a development shell along with direnv makes for a very nice developer experience.

The thing is though, you can get these benefits even without using NixOS, you can install Nix on various Linux distros and personally I use it on macOS.

NixOS is great for servers where reproducibility and consistency is important, personally I was never a fan of tools like Ansible that are a bit of a hack.