For an N/A Forester your best bet is to go with OEM filter, but if you really want to get yourself some better intake, meaning cleaner cooler air with more oxygen in it i would then go for a full snorkel. I have had my snorkus removed to the airbox and just stuck a foam filter on the end of the box with a clamp as recommended to me by a mechanic who has worked on some of the worlds best rally cars and had no other filter in the line, what did this do? made the induction sound real noisy and didnt give me anything i could really see worth the effort, remembering rally mechs are looking for 10ths of seconds we are not. Same as expensive an aftermarket filter as opposed to OEM, there are no gains there you are going to notice, other than your wasting your $$$ on expensive filters.