I found that the nix learning curve to be steep but short. The first time you need to make something available for nix (particularly a service), you'll probably copy something someone else wrote, make a few changes and then (if it didn't work) stare at your screen for a while wondering why it didn't work[1].

It is very different which can be very off-putting, but is not usually gratuitously different, and once you get used to it, it's pretty straightforward.

After having done it a few times, I find that I can adapt a random project not already in Nixpkgs for nix in under an hour, and it's something I do maybe twice a year or so.

One counterintuitive advantage I found switching to nix from other systems is that since the 4 step "download, configure, make, make install" usually doesn't work, I take the time to make a nix expression. On Gentoo and Arch, I would often just install to /usr/local from source and then forget what I had installed and not know how to upgrade it. If you have more discipline than I do, then it's a bug not a feature, but for me it's super helpful.

1: If the project uses cmake or autotools and has no strange dependencies, then packaging it for nix is trivial. However a surprising number of packages do things like downloading dependencies from the internet at build time, and it's not always immediately obvious how to adapt that to nix. Projects using npm or pip also probably won't work right away just because the long-tail of dependencies means that there will be at least one dependency that isn't already in nixpkgs (haskell should in theory be just as bad, but the strange proclivity for haskellers to use nix means that someone has probably already done the work for you).