Personally, I use NixOS in conjunction with Home Manager[0] to more conveniently use Nix to manage my user-level config. The configuration that I manage with Home Manager includes my Emacs config, my Git config, and my Bash config. Additionally, almost all of the other programs I use on a daily basis are at least installed through it. Since it’s primarily only used for managing some packages, the configuration process was simple compared to setting up NixOS for me.
I would imagine that you could use Home Manager on a non-NixOS system to at least create reproducible configs for the programs you use, although the OS as a whole would of course still be non-reproducible. However, I do not know how well Home Manager works on non-NixOS systems.
As you mention, just using Nix itself can be sufficient to get a reproducible set of packages on your system. I recall reading a blog post about someone who does this on both Ubuntu and MacOS.[1] The way this person does it is interesting because it’s more sophisticated than spawning the occasional ‘nix-shell’ or something. For example, they get the benefit of Nix “generations,” with a new generation being created each time they modify their declarative config files.
I've found home-manager to be more trouble than it's worth for most things:
* Config files aren't always stored in text (e.g. KDE Plasma, Gnome)
* It's all-or-nothing usually, unless you can find a way to make the home-manager config your "base"
* Changing settings isn't integrated, and requires editing/rebuilding/reopening (e.g. I can't just hit Ctrl+ to increase font size in VS Code, I have to edit a config file, run home-manager switch, then usually reopen)
* Plugins, especially things like extension stores, are a hack and a half. You have to hunt for hashes, then change it every time your old version falls off the CDN.
It's a nice idea, in theory, but it only works in a vacuum.
I would imagine that you could use Home Manager on a non-NixOS system to at least create reproducible configs for the programs you use, although the OS as a whole would of course still be non-reproducible. However, I do not know how well Home Manager works on non-NixOS systems.
As you mention, just using Nix itself can be sufficient to get a reproducible set of packages on your system. I recall reading a blog post about someone who does this on both Ubuntu and MacOS.[1] The way this person does it is interesting because it’s more sophisticated than spawning the occasional ‘nix-shell’ or something. For example, they get the benefit of Nix “generations,” with a new generation being created each time they modify their declarative config files.
[0] https://github.com/nix-community/home-manager [1] https://www.nmattia.com/posts/2018-03-21-nix-reproducible-se...