I ran this for a couple years on my Edge 600 RMK, but just put my stock silencer back on, and glad of it. Ultimately, this is just too loud for me no matter the gains: I felt like I needed to wear ear plugs on longer rides, and I don't think I made any friends with it. It's not that it's deafening at WOT, just louder across the range with an annoying drone at 30-40 MPH. Really, unless you're just looking for noise, the stocker sounds better on all counts.
In terms of gains, I'm partly guessing here, but I'd say they're minimal. It is lighter, but the difference is surprisingly little given how much bigger the stocker is. You may get a few horsepower, but not enough to be worth it unless you're pushing the ragged edge.
The only good things I have to say about it are that the finish has held up well and it does give you more space around the chain case. Overall, the only person I could recommend this to is someone to whom noise is truly not a factor (maybe someone who only rides on private land with ear plugs?).