That thing is just a resistor inside a little fancy black plastic box.
Putting a resistor inline with your Intake Air Temperature sensor will fool your
computer into thinking its colder outside than it really is, and it will add more
fuel for what it thinks is the more dense, colder outside air.
You can go to Radio Shack and get a 35 cent resistor and do the same thing.
But be aware, that you are adding more fuel without really actually adding
in any more air, which makes your car run really rich.