While I don't use Debug mode very often, I certainly find it convenient to do so with this simple add-on.(vs. Starting an FTP program, Starting an Editor program, Opening, Editing and then re-saving config.php)
Absolutely essential to my every day work developing on a live site. Normally I would IP whitelist the config but it gets tedious. The only way this could be better is if it allowed configuring users to be enabled for. Either way its still an essential item.