There's a lot of controversy as to the effectiveness of higher flowing filters. Generally, they will let a bit more grime in because they do have larger openings in whatever filter element is used (foam, paper, wire mesh, oil)... some companies advertise life-long use but you have to use special oil to coat the filter in order to keep it effective. Since they are so cheap, I usually change filters every 10-15,000 miles, which is probably way to early. $25 for a genuine K&N cone on Ebay really isn't that bad (it sure beats the $60 you'll fork out at a retail joint!).