Has anyone used QuidCo or TopCashBack to get money back on their online purchases?

Has anyone else on this site ever heard of or used QuidCo or TopCashBack to claim back cash when buying stuff over the internet, those sites were recommended to me by someone on “moneysavingexpert.com” but as you have to supply them with your bank account details In order for them to send you cash back on your purchases I am understandably wary – on one of my purchases I would be sent £40 back so I am eager to use their services but only if I am sure they are legit, so has anyone else in Britain had experience of them.