Dan - you hurt my feelings!!
I bought THREE of those for the 325i. One for the intake, and one for each exhaust tip. I am now getting 45% more power (15% x 3 devices) and 40 mpg. And you should hear the ear splitting whistling sound it makes from the exhaust vortex. Sounds just like an F16 taking off!
I am noticing one problem though, the improved intake airflow is so strong that it is tearing the air filter apart!!!