Would it be a bad idea if he kept using that Hidden Admin User account?
I do not advise using the Hidden Admin account as your daily use account.
It circumvents much of the security in place (like IE protected mode) and is unable to install certain Windows Updates security related updates.
Furthermore, the Hidden Admin user account is your last line of defense in a system recovery, permission setting issue(s), etc... and if it becomes corrupted, you're basically screwed with the only way out -- reinstall Windows.