More likley then not its one of those bullcrap devices that just trick the coolant temp sensor or the air intake temp sensor into always telling the ecm that the coolant or air temp is low (ethier with a resistor or possibly that switch which just shorts the sensor circuit), thus cuasing the ecm to adjust the fuel trim for such conditions and adding more fuel to the engine even when it doesnt need it.
Ill agree that possibly under certain condtions the extra fuel charge may possibly warrant more power out of your motor...however you would probably need to be driving with a lead foot for the engine to make use of the extra fuel, and even in that case it wont really be worth the extra fuel your burning, more so with gas prices the way they are. In addition, the times you arent driving like a 17yr old who just got his license, the motor will still be running rich, burning more fuel all the time...and eventually possibly cuasing premature carbon build up, fouled sparkplugs, and a constant extra load added on the catalytic converter(s).... for those of you with state emissions testing that alone should raise some concern....catalytic converters run a premium to replace not matter what you drive. Just my 2 cents
