(Side note: NixOS deserves its own subforum, obviously. It's more popular than most distros with their own subforums here)

What do you think about NixOS? What was your experience with it? Any reasons to prefer it to Debian Stable?

Personally, I think the idea of "reproducible systems" is great. Also I kind of know (but don't use) Haskell, so learning NixOS's config language should be easy. But, it just seems strange that you need to learn a programming language to use an OS. Also, some people are saying the security is not that great (hearsay). But their Security Team is just 2 people, and I don't know if they are working on this full-time or during lunch breaks or what.

According to Repology statistics, NixOS doesn't look that bad. Of course, Repology statistics should be taken with a grainpound of salt as any automatically collected data. E.g. their vulnerability counts are most probably wrong: distributions like Debian or RHEL backport security fixes to older versions of software rather than letting new versions into their stable releases. I guess Repology bots cannot account for this and end up with many false positives.