I have used Quidco for a few years now but their service has gone downhill fast. I know of several people who have had their accounts closed and "on hold" for months without any reason provided whatsoever.
This usually happens when they have gone to claim a payout which, in some cases, have been hundreds of pounds.
I would suggest that everyone stick with other means of discounts and cashback i.e. Student discounts (Student Beans), BlueLightCard, cashback DIRECT from the retailers themselves, Google Shopping (most of the time there is more discount offered UPFRONT here than with Quidco or TopCashBack) or codes you can find online.
I won't be using Quidco anymore in any case.