Been using this for about 6 months now. It's great. Not loads of retailers but defiantly ones I used weekly. You link your cards to it and then it picks them up when you use them (online or in store and even when it's via PayPal / Apple Pay etc)
Cash back is generally a bit higher than quidco / topcash back etc and not so long to pay out.
74XGYHJX is my referral code.