If it's the one i've seen, it's not a fan, it's just a piece of metal with some fins that supposedly force the air passing over or through it to "swirl". Yippee! I think their only hope is that by the time you figure out that it isn't helping, your wife has thrown the box away and it's too much hassle to take it out and send it back. Either that or you'll be so concious of it that you'll be "easier" on the gas pedal and you will actually get better mileage i.e. a self-fulfilling prophesy.