I dunno where the idea of shortening engine life comes from, unless I've got this thing completely arse about face.
It goes in the air temp sensor wiring making the ecu think the air is cold, so it adds slightly more fuel (cold air = more dense = more o2, with correct air/fuel mix = more power).
Problem is, the air temp sensor is really there to help the ecu decide on the fuelling. If this device causes the ecu to add more fuel the lambda sensor will very quickly pick up an over rich mixture and tell the ecu to back it off again.
So you gain nowt, just make life more difficult for the ecu as it's running without one of it's sensors.