As a Home-Manager user I would argue it’s not really worth it. It has it’s moments for some applications but most of the time it’s the same experience as editing the config files directly. Except instead of INI or TOML it’s stringly typed Nix attrsets and you need to rebuild the entire system instead of restarting the app. Not exactly a huge improvement.
And that’s when you’re lucky enough that what you’re configuring can be mapped to attrsets. Styling Waybar via Home-Manager means writing CSS but it’s a multi line string in Nix with no appropriate editor support whatsoever, and writing custom actions for Nixvim means writing Neovim-Lua but… that’s right, in a multi line string.
On a more positive note, I will second the recommendation for the NixOS & Flakes Book, I found it to be much more useful for getting my head around flakes (and Nix in general since I started using them fairly early on in my Nix journey) than e.g. Vimjoyer’s videos, which are good but their repositories were really really cryptic to me at the beginning.
The matter of flakes is complicated. Yes they are experimental, but in reality most Nix users use them despite that. I’m a bit on the fence on whether you should start with flakes because they do add some complexity. You can copy paste a sample flake configuration from the Internet (there are many but they all do exactly the same things) and you’ll probably be fine but telling people to just copy paste code they don’t understand feels wrong as well.
Regarding documentation… I wouldn’t go as far as saying you should avoid it entirely but it is in a very unfortunate state with a lot of wiki pages being outdated or just containing snippets that do things in very weird ways, or are over engineered to the point of being incomprehensible.
And that’s if someone bothered to write up anything at all. It’s a bit sad but reading from the nixpkgs GitHub (or other people’s dotfiles) is sometimes the only way to get certain information, such as valid values for package overrides.