There was an item on cheque back offers on Watch Dog (BBC1) a few weeks ago. The upshot was that many of these companies go bust before the time span on your offer and you don't get the cheque, others rely on only a small % of people asking for their cheque as they do not send it out automatically, and then you have to follow the instructions TO THE LETTER otherwise you do not get your cheque. If you manage to get through all of that they then delay posting withh all sorts of excuses every time you ring hoping you will eventually give up. Just a note of caution.