Whilst I can't comment on this particular seller, unfortunately, you cannot trust feedback as far as flash memory is concerned... Look at eBay, for example - most vendors of fakes there have sterling feedback records, and that is due to people not testing their cards/flash-drives and thinking that copying a text file to it constitutes making sure it works properly, and thus giving positive feedback as a result. (Many don't learn they've been had until much later, sometimes years after the fact, when it's far too late to do anything about it. And others believe the line about the goods being "faulty".)
Moreover, Amazon's own price seems to be cheaper (£25, as opposed to £40-ish) anyway, unless I'm severely misreading something...