I have a dual n1. Not really by choice but because it came with the car when I got it. All I had to do was bolt it up. I like it the sound. Its not bad, and it looks pretty good w/ my car. Its really deep. And u can really hear the turbo, its kinda like an open downpipe but muffled so that its a really low purr. But I also have straightpipe. No cat.
I would have chosen the HKS though had I built the car.
I have a video from when I was troubleshooting my car and u can hear my exhaust.
http://uk.youtube.com/watch?v=lzlcoGMfUz8
As for looks I tucked mine away, shaved the bumper when I mounted it.