I've bought over 90 computers and lappies from PCW so that alone should speak volumes. They have the distinct advantage that you can walk away with the computer.
I would refrain from buying either the power surge protector (much cheaper elsewhere and many computers come with adequate surge protection) nor the Norton or MacAffee 'security suites, AVG MS Antispy and any old free firewall will provide you with more than enough protection and they all cost de nada.
I would also not go for the '3/5 year protection warranty, it is expensive and your household insurance and consumer rights cover the same. On the few occasions that I have needed to take something back they have always been helpful...but then I am always polite and do not march in with a bolshy attitude and a face like a wet weekend in Huddersfield.