Hmm, I had a friend who became one of their reps and so she encouraged us to sign up. On the face of it, it seems like you get money taken off your utilities bill for shopping in certain places, but for us (tight arses who shopped at Aldi and Tesco!) it didn't save us anything because the shops which were affiliated were things like Sainsbury's and Boots where we didn't shop anyway.
While we were with them it was fine, the problem came when we tried to leave - I phoned up and asked to cancel our account, which they did, but it apparently didn't occur to them we wanted to therefore also cancel the cashback card (why would we keep that if we didn't have our utilities with them?!) so they charged us for that for the next month. We phoned, cancelled the stupid card and paid the 2 pounds or whatever it was, then got ANOTHER bill for some other thing (which as far as I was concerned we didn't owe as we had already had our final bill from them (stated on the invoice) - this extra was about 10 pounds). This went on for ages, they wouldn't back down, neither would we, they sent us more bills charging us interest on the amount they said we owed, then another bill for some other 'remembered charges'. After a LOT of phone calls , they finally gave up.
Incidentally, my 'friend' when I asked for her help in resolving this wasn't interested. Probably because we were leaving and she's only really interested in signing people up. Her FB is always full of 'it's so nice to know that when I shop I'm saving money on my bills'. Ugh.
So my experience was mixed. Customer service for us certainly wasn't great.