I found this interesting. I picked dup NixOS a few months back using configuration.nix and home.nix and completely avoided flakes all together because it was an experimental feature that will have breaking changes going forward.

I feel like this book jumps into flakes too soon. it should have more around the configuration.nix file, its purpose and uses, and then show systematically why one may need a home.nix file and then maybe show why something like configuration.nix/home.nix might not serve some users (and then introduction flakes for those individuals.)