I was a member of Quidditch from 2006, when it claimed to be a "Cashback cooperative" with an active forum. I then joined Topcat, which was the free to use "also ran" at the time. I looked at a few other CB sites and tried one or two, but they either seemed to be scams or the offers were insufficiently attractive to me.
Then Quidditch started to change and become the monolith it is now -all talk of "cooperative" gone. Topcat hit issues with fundamental changes and the failure to chase merchant offers (insurance) - then started to copy Quidditch in terms of paid access, etc. I lost a couple of fairly large payments on both sites and became frustrated at the lack of response and eventual suppression of the forums. So my use of the sites dropped off - to the point where I started to look around for an alternative.
I really don't remember what it was that caused me to try imutual, but it seemed to be the answer to the issues I had with the other two. Actually, the response to queries and overall "feel" of the site was better than the others had been and the forums were not purely focused on offers and issues with cashback. So I changed to use imutual as my primary site and only use the others if they have offers that imutual can't duplicate - and even then I allow imutual a large margin, because I actually trust that I will see my cashback at the end of the day - a confidence I had lost with the other two, having missed out on fairly large cashback payments (remember the days of the big insurance offers ?