i have just fitted a new GPR Aprilia Atlantic 500 Exhaust Slip-on Stainless Maxi Streetfighter, it looks excellent!! it doesn't sound much louder than the original with the decibel killer (baffle??)in place but once removed it sounds great!! although not legal for our roads

it was pretty easy to install, AFTER i had thrown away the instructions, which were a bit confusing to say the least!!
i will, if anyone is interested, post a couple of pictures after i have been out and tested it

cheers,
Don.