No kit is any good if it sucks the engine bay air, from behind the rad. Most kits just slap a pathetic foam cone filter on the end of the MAF tube and "good to go"!
You will notice the stock setup draws cool air in ahead of the rad, that is the MINIMUM an aftermarket must do. The best setup I've seen is the Racing Beat, with the enormous scoop behind the front grille.
Hobbies: Filling in questionnaires complaining about Jarman Mazda.