There are alot of totally enclosed filters these days, BMC CDA, Pipercross Viper, K&N Apllo to name but a few, its quite hard to compare performance with these filters as on rolling roads they have been know to lose bhp as there isnt the same kind of air flowing into the filters on a rolling road as there is on a open road plus the car is stationary on the rolling road and is only being feed via a fan.
And becuat these type of filters are totally enclosed they totally relay on their direct cold air feeds for all their air supply hence the lose in performance on the dyno machines.
Which is best out of these? Hard to say really, if your happy paying the extra then do if not by a slightly cheaper item.
Contact
www.kam-racing.com as they sell BMC items, compare prices with them if you havent already.