Hello!
Installed it on an old laptop and tried setting up a Node. Would have worked out of the box without any problems except that I didn't have enough storage for a full node. Allegedly very secure because everything is compartmentalized, i. e. no conflicts with dependencies etc.
You have a config file. With that file you can set up the very same system on a different device or roll back to a previous time if you accidentally break your system. Nix is not only an operating system but also a package manager like apt is for Ubuntu. It is functional, meaning that there are no side effects: The same config files gives the same outcome.
If you install Nix Bitcoin on NixOS you just reference the template on the Nix Bitcoin Homepage in your config file. You could also use something called Flakes but I know little about these and didn't use them.
You can also set up Nix Bitcoin on a different operating system as far as I know by installing the Nix package manager first.
You can also modify the template config file to your liking, e. g. compiling everything from scratch, but learning the Nix programming language involves a steep learning curve supposedly.

Hope that helps, a pleb