> Another underappreciated feature about NixOS is, that you can create a VM out of a NixOS config to locally test a server update/deployment.

And similarly, you can generate a bootable ISO of your NixOS config. It's really nice for both testing things out and also as a recovery mechanism. Rather than booting some generic ISO, connecting to the internet, installing whatever recovery tools and filesystem drivers I need, and then doing the recovery, I can boot an ISO that is identical to my main system, with all my favorite recovery tools pre-installed.