Last week i have installed the Akra on my Duke. Without the silencers it sounds nice, but when you open the throttle, you become deaf. With the silencers mounted, in idle the sound is not loud enough, but again when you open the throttle, it is hard. The tone is higher then I expected. More like a dragracer with open exhausts.
I have made the silencer half the lenght and reinstalled them. Still to soft, now I am running with 1 silencer mounted and one out. Now the sound is nice and it doesn't make me deaf. No landmower anymore.