Definitely save your cash for something that actually works. This is in the same class as clamping a magnet to your fuel line to "magnetize" the fuel and make it atomize better. Take a look at the JC Whitney catalog some time, if all of these contraptions actually worked, we'd all be getting over 100 mpg on our cars.
Remember, there is no such thing as a free lunch. Save your money.
2004 Vivid Black Road King Standard
2004 Sierra Red FXD -Gone, but not Forgotten