I'm in Australia and it has never worked. I tried it for a while but after it never found any deals I disabled it a while ago, but enable it every now and then when buying something online to check if it is going to find any deals and it never does.
From what I've heard it works in North America. I'm not sure if it's just a difference in the American market where coupons and discount codes are more common or if it's something to do with the way it works where there's more users in America which allows it to find more deals, or what... If you're outside of USA/Canada then I don't think there's much point installing it.