NixOS for busy developers ain't for the faint of heart.
But I am extremely faint of heart, and I love NixOS.
The trick is that I'm not a developer, and I happen not to need to ask it to do anything complicated or non-standard. I expect lots of other people are in my position (although maybe not many of those people read HN).
OTOH it finally got me over my fear of being a n00b and just use the source.