I hate it when someone buys those things.
Here'* the deal. The IAT sensor does affect performance. When you trick it into thinking the air is cooler (denser) than it normally is, the PCM will demand more fuel. You'll feel the performance increase right away.
Over time (less than 100 miles) you will slowly LOSE that performance gain, and it'll be gradual enough that you don't even know it. Why?
Ok, I'll tell you.
Your MAF sensor and O2 sensor aren't stupid. They'll see you running too rich with a specific amount of airflow, and they'll lean out the mixture. Your PCM will learn the proper A/F curves. Sorry. The only way to fool it is to actually decrease the incoming air temps, or increase the volume. Hence the CAI.
You could have performed this short-term mod with a 25-cent resistor from radio shack. But it wouldn't have done you any long-term good, either.