The add on button helps ensure that I buy through MrRebates without specifically going to the website/store through MrRebates. That's a good thing since I've sometimes bought too quickly and forgot.

HOWEVER, the MrRebates "reminder" places itself directly over the typical place on the page where I'd log into the store account and even after I click through it sticks there making it terribly difficult to log in to a store's account. Annoying to say the least!!