The problem with Kelkoo & its Price Runner rival is that they offer a very limited selection of retailers. The bargain they offer is not infact what it seems - its the cheapest from a few.
Many of the sites offered up tend to be uncompetitive multiples, or increasingly these days, the internet names of high street shops (Drill down to the bottom of terms & conditions and note ownership - then go onto the Companies House Register and check who really owns them!)
For example digital cameras on ebay offered new from Hong Kong come in with an extremely attractiive base price. However, add their often expensive postage costs, the fact that VAT (duty is a very small percentage, contrary to what most people think) is added to the original cost PLUS the postage & duty, then the Post Offices levies what is laughingly called an "administrative fee" (£8 - £20) and the bargain suddenly vanishes.
Couple that to the fact that the importers won't touch the good with a barge pole (why should they - British law says the retailer is responsible!)and the disadvantages of buying new through overseas channels is diminished. Another problem is the exceedingly short life cycle of goods, the unavailability of spare parts within six months of purchase and suddenly, a conventional sshop that retains your right of legal redress becomes increasingly attractive.
Me? I now go in to major retailers like Jessops, brandish the cheapest ad I can find for the product and they normally match it!
My feeling is that the only true bargains are the ones you create for yourself.