I use the UNI filter and my understanding is that the UNI, lightly oiled, is less restrictive than the stock paper filter. I tried the UNI before rejeting and could tell a difference. The UNI made it clearer more fuel was needed in the mixture. After set up right, you might not notice the difference. I feel it helped and is worth it, especially since I don't want to drill the bottom out of my airbox.
