I think they're a fairly common kind of slipon.....my bike came with them and heard lots of others that have them as well. They're fairly light cans, probably save a good 20lbs or so from the stock muffler which is a total brick.
Power is negligible with slip-ons, but at least the Holeshots don't kill it from stock like the Cobras. Rejetting to 147.5 mains seemed to crispen up the top end a bit on mine, which had the stock 150's in it. The p/o dyno'd the bike, with holeshots and a not-so-great setup with the stage 1 kit it spun a 114.5hp....or pretty much exactly stock. I've since fiddled with it and it seems to overall run better, so maybe it's up to 115 now. It's splitting hairs.
You could probably modify the cans to be shorter if you wanted to, which would make them louder. Diameter of the opening has the biggest effect on noise, but length of the can makes a difference too, longer being quieter.