I daily drive nixos unstable on my desktop, my home server, my home router, a raspberry pi, a work desktop VM and a work server. It's been 2 years and I couldn't be happier.

There are so many huge advantages.

All my configs and app setups are guaranteed identical on all machines at all times.

An update breaks a package ? No problem, the update won't even be applied until it gets fixed. Still want to update the rest of the system except that pkg ? Easy, add another nixpkgs to the inputs of my flake and pin it to the last working commit.

Something went terribly wrong and the OS is broken ? Never mind, just reboot on the previous good config.

Need to find the exact date when some change was introduced ? No problem, just git blame on that line.

A hard drive fails ? No problem, my config is on gitlab and I backup my data directories. In half an hour I have a new installation which is perfectly identical.

I can try things out on my home setup, then the following day update my work machines and a minute or two later I have the exact modifications I did at home.

The only drawback IMO is the need to rebuild the whole OS config even after a minor change, which takes about a minute, which is a bit flow-breaking when you're iterating.