^ Which is pretty silly, when you think about it. You pay (whatever) so that something else can push your foot down a little harder (and a couple of milliseconds sooner). There's no change in tune and no change in top end output or engine efficiency.
Actually when you think about it, in a manual it should make fuel economy worse because it'd be opening the throttle more than needed for efficient acceleration. In an auto it may be different ...
I posted some time ago the difference in fuel consumption in my auto from 0-50km/h at a nominal 2,000rpm and at 2,500rpm (yes, only a minor difference but it's at a vital point in the rev range). You'd think that at 2,500rpm you're going to be using extra fuel - and yes, you will - but in the auto, the torque converter is right near its "stall speed", which is the point where the TC will not lose as many RPM in the transfer from engine to gearbox. The end result was that accelerating at 2,000rpm used less fuel but wasted so many RPM and took longer to get to 50km/h, so in the end used more fuel to achieve the same goal. The Windbooster/iDrive/whatever will actually assist by forcing your foot down harder and giving the same result.
The best advice I could give - use your own foot and save the $.