Wouldn't use them again
I had a poor experience with this retailer, apart from the prices which are good. I do not think they would be able to resolve problems or cashback in a fair or timely process based on my experience dealing with my order problems.
They first messed up my order details, then had to confirm it on the phone (which invalidates cashback) and required lots of security steps (including needing a copy of my signature). Then they delivered half the order with the remainder lost in their warehouse, and finally lost correspondence between us. At all points you have to deal with an uncommunicative and unhelpful customer service team, I suggest minimal chance of getting cashback despite it tracking quickly, based on my experience!