Yes, but while I can create a custom NixOS ISO that auto-install on my desktop my final production desktop I can't do the same with OSX or Windows, I can craft a big infra with very expensive proprietary software, largely overkill and still my system would be a hybrid. *BSD allow custom ISO, so most GNU/Linux distros but they are FAR more complex than a simple file and nix-build '<nixpkgs/nixos>' -A config.system.build.isoImage -I nixos-config=iso.nix to create the image.

I've used a discrete set of OS, back than also Irix (an old O₂ given to me as a teenager), Solaris (9, OpenSolaris SXDE, SXCE and OpenIndiana), I've tried Nexenta (IllumOS based on Debian userland), Milax, Belenix, FreeBSD, OpenBSD, various GNU/Linux and Windows. NONE of them have the simplicity of declarative OSes like NixOS/Guix System and I insist, -OS/-System because just the package manager it's not enough.

I manage infra with Ansible, Fog, Saltstack, have used cfengine and puppet in the past. None of them can compete.

The reality is a terrible sorry state of things. NixOS/Guix System are the sole LESS ugly for the modern time then the rest, like zfs for the storage confronted with anything else, hammer (DragonFly) included.