Guix is a reimagining of the concepts of Nix with Guile/Scheme instead of the Nix language, so they are very similar in overall feel, but differ in the details (e.g. GNU Shepherd vs systemd).

As for learning curve, I find Nix substantially easier, since the language is much simpler (JSON-like with lazy-functions) and doesn't need all that weirdness that result from using Scheme as configuration language (lots of quoting, module system, etc.)