"InvisibleHand scours the web for better deals on the products viewed. Its big advantage over comparison websites is that prices are gathered "live", whereas sites such as Kelkoo and Pricerunner list prices provided by retailers at intervals that may be out of date when you search." Times Online 
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"This week we tested it on some popular purchases. First, we visited johnlewis.com to browse TVs. When we clicked on the 32-inch Samsung LE32B450C4W LCD HD-ready digital TV, a yellow band appeared at the top of the page telling us we could buy it for £298 on the Pixmania website - £51 less than at John Lewis." Guardian
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"I'm addicted to its unobtrusive, deal-finding prowess" Gizmodo.com