I share your frustrations with some of the data but it seems to be more accurate with smaller value items. At the end of the day, it's better than nothing. Can you suggest something else?
Just looking at a new Dell XPS laptop ( with a touchscreen ) and a very similar/better spec than the new macbook pro. They have 12% off until Monday and the price is £1000 less than the new macbook so it looks like Dell will get my credit card details.