Useless? let's be a bit more fair with the advice and let people make their own decisions. Unless of course you have the data to back up the claims.

We ran our CAI on the 323 for 50K without issue (cleaned at 30K). I also run them on the motorcycles too. While I have not done a before/after dyno, the throttle responsiveness is definitely there.

Of course, air quality must be taken into consideration, but if you see an X5 off road for more than a few minutes, take a picture, no one will believe you.