green cotton and k and n are all open induction kits,, which means they roar when air is being sucked through them.. bmc and the like of enclosed induction kits suck lots and lots of cold air meaning much better performance gains, but not as great a sound..
depends what yur lookign for really.. both has advantages and disadvantages..
if you want speed but not bothered bout sound they make then go foir an enclosed..
if u want sound but not bothered about performance then get an open filter..
the open filters are much much cheaper then the enclosed ones.. your choice..