I've been on nix for only 2-3 days so take what I say with a grain of salt. I think it's pretty useful. Back in Arch/EOS, I always find ways to mess up the system (I switched to Nix because of a failed system update on EOS). On Nix, it's so easy to roll back and you don't even need to use the terminal.

sudo nixos-rebuild switch --upgrade

There are (afaik) 3 channels you can choose: stable, unstable, and small(?). I'm staying on stable for now. Package manager is slower than pacman, imo, and it's not as straightforward as Arch. Some programs (like kde connect) need to have service enabled in config.