they claim a rediculous horsepower gain... i'm really not sure where they get the validity to say so, but 99% of people will only experience a couple hp gain. but then again, it's not like it's that much more than a normal filter which you would have to pay for anyway. i think they are worth it for the most part just as good car care. it's just like wiper blades... you can buy quality blades and never have a problem with water or you can get normals ones that start to go in a month or so, if not sooner.
another to check out though is Accel Kool Blue filters. that's probably what i'm going to use when i get a new car (whatever that car may be)
http://www.mrgasket.com/koolblue/