I've seen this before.

What it does is tells your car that you're seeing colder air than you really are, so the computer compensates by spraying more fuel into the cylinders and keeps the timing advanced instead of allowing the normal conservative ECU controlled timing to stay in effect.

Bottom line: you'll burn more gas, but you won't really get the claimed power, the only way to safely and consistantly squeeze more power out of your setup would be to get an honest fuel computer instead of a little box that lies to your engine and claims power. The only real truth I saw in that was "watch your 1/4 times increase". Now tell me, who really wants their times to increase?