I've been using keepa.com for years and really like it, but the add-on doesn't appear to work, at least out of the box. Reading some comments it seems I might need to lower some security feature for it to function but none of the things I tried worked.
If the add-on needs extra steps to actually work, that should be mentioned on its front page and/or app settings!
Also, I'd expect at least clicking the add-on icon while I'm on a product page would go to Keepa's pricing history on that product at least, but it just loads my tracking list.
So, right now, the add-on has no use at all for me, unfortunately.