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!

I really like the shopathome.com add on. They usually pay a percent or more than the other money back services do.