You'll get a lot of opinions.
Maybe gain a hp or 2.
There's been a rumor floating around for years that you can lose a hp or 2 with an aftermarket filter...yet no one ever posts dyno results to prove it. And last time I checked, more air in and more air out, tuned, means more power(even if it is just a little).
So, before anyone else brings it up, bring your dyno proof with you.
I had the K&N, and later a BMC race in my gen2(BMC Race was about 2/3 as thick as the K&N). You can hear the difference from under the tank immediately, so the engine is able to breathe easier. The off idle throttle response felt better than stock too.
Best thing though is that they are reusable.