that's true from the forum operator's point of view. the user basically gets rid of the popup and continues to use the site ad-free! even if he misses some or the other error message, the add-on's effectiveness is lost
that's why i had been wondering if it was possible for you to tap into the xenforo's internal
User discouragement and discipline functionality. use this function for ad blocking members while showing them the message why their experience on the forum is so messed up.
probably a crazy idea though