breather filter is a waste of 14 bucks if you take care of your whip.
if you have horrid emissions however.....
breather filter replaces a hose that runs from your engine head back to the intake pipe. this hose recirculates unused air brought in from ECU controlled air/fuel ratio combustion. this air that is sent back to the intake pipe is HOT!!! and dirty engines generally send back carbon fouled air, low in O2,....did i mention HOTTT!!!!
now, this is a small amount of air mind you, not significant for naturally aspirated systems, and its a one way, so using the hose wont rob you of power.... so in essence, the breather filter looks cool as nuts, but ineffective to performance.
additionally, breather filters do NOT come with a cap for the intake pipe side (you know, the side that has a FILTER on one end to keep crap out) so many will try and tape it off....poorly, and ultimately let in more sand, gunk and crud into their intake system that the breather filter is keeping out, so its not that effective to just try for show, and end up with half-assed taped up sections of your pipe.
keep the hoses friend, color match important pieces if you want show