I remember when I was a kid, My dad getting into 3-4 shops to find out which shop is offering the lowest price. Well we do it still today in India as online shopping is not to so common but if you are in UK, US or Germany Invisible Hand can just help you out.
When you are websites which sell products, Invisible Hand gets busy in finding offers for the product in the background, before you even think of buying it, the best deal which is low on price is offered to you. This helps you save money when doing online shopping and If you are on a deal which is lowest, it just tells you that.
The best way to use this service is using the Addons which is available for Firefox and Chrome. This is the most efficient way to find out best deal because you do not have to do any comparison or any bargain, it just gets you there.