After reading this thread, I hate to admit that I did purchase one of these and install it in the quest for more HP and better MPG's.
It did seem to add some pep to the engine. The MPG's did not improve though even with easy driving. The onboard MPG checker got fooled by this gadget. I was double checking my mileage with an iPhone app and it did not improve, actually got worse. I have taken it off.
Just glad I didn't spend any more than I did on it!