They seem to use Amazon Marketplace to do their order processing. They're probably okay, but I fnd it a bit strange that there seems to be no information on their website as to who they are, no address, email or phone number, and I'd want to make sure Amazon will guarantee the purchase before I ordered. In any event, you should ensure that the checkout/payment is done via Amazon's system - see Amazon's Marketplace info here.
I found this thread about them on another site - I assume the £324.40 postage charge was some sort of a bug!!!