I'm running home-manager on arch and it's fantastic. I'm only using it for cli/tui programs, as I've had trouble getting gui software to correctly create desktop entries which show up in my menus. You can use it alongside pacman just fine.
targets.genericLinux.enable = true;
xdg.mime.enable = true;
xdg.systemDirs.data =
[ "${config.home.homeDirectory}/.nix-profile/share/applications" ];