surfer boy

I have seen a few adverts for a device called "motoflow" which clamps to fuel pipe after pump and which puts a magnetic charge into the fuel, allegedly improving fuel consumption by upto 20% by allowing better combustion. Has anyone fitted one at all as I'm keen to try anything that helps cut fuel bills. The web site has the usual testimonials from satisfied users of everything from truckers to boat owners. But for £50 it sounds too good to be true - is it?