http://codex.wordpress.org/Plugin_API/Action_Reference/user_register
The question you referenced uses the ‘register_post’ hook which is just before the user gets entered into the database. If the registration is successful, that is when it sounds like you want to redirect. So, use the hook that fires immediately after the user is entered into the database.
TL;DR Use the ‘user_register’ hook instead of ‘login_head’