It annoys me so much when they continue to dribble on about how you can return things and so "lose nothing" if you decide you don't like. I can't be the only one who shouts "two lots of P&P" at the screen.
As said before you need to be pretty sure you will not return an item and the add on the P&P to judge the value. Indeed I think it is unethical of them to keep the P&P separate. It isn't as if you can opt not to pay it or that hey have a capped P&P. They should quote the total and then the deductions for multiple purchases.