This extension has a terrible memory leak with Firefox. It caused my browser to go from 30% memory utilization to 95% before firefox ran GC. It made the browser really slow and even unresponsive during GC. I started removing extensions to troubleshoot, and found this one to be the culprit. Now my browser is running better than ever.

Avoid this kind of useless shop-savings extensions that in facts can spy what you are looking on the internet, it's just collecting informations on you to profile you and similar customers to finally target ads/products/services. That's desguished spyware in counterpart to provide you a pretended nice service for free.

And just about the service provided: this kind of extensions (lots of similar exist like this one) can modify the webpages on-the-fly and also can censure some parts or search results to guide you to buy to a specific shop... instead of a concurrent. And guess who is paying the extension editor to do that? Sellers?
Just look at what this extension is requiring at the Permissions part...

Mind again before adding browser extensions!

For all their hype they are definitely wanting. I realize they can only pass on what they have negotiated with their sponsor stores and for which products / categories of merchandise. I spent over $1500 on various items this Christmas to try them out and got back a whopping 31 cents. Don't waste your time.