I've finally heard the the Two Brothers exhaust this weekend. Saw them Saturday at a gas station on a Ninja 636. Should be comparable since its a four cycinder with a dual underseat exhaust too. He didn't have any power tips in. I heard him pull in, heard it idelling, and heard him leave. After reading about the reputation Two Brothers has for being loud I was surprised by how mellow (not loud), but nice sounding they were.
I heard them again Sunday on a different Ninja 636 while on a group ride. This guy also had no Power tips/ DB reducers on his system. I even ended up riding behind him for many miles. I didn't think they were even that loud, let alone too loud. It was a mellower ride, so he wasn't riping on it much. But I couldn't notice his noise over my own wind noise.
I think I might end up getting some now that I know that they're not obnoxious. By the way, These guys said they paid $1200 to $1700 for there systems. The cans look the same as ours, but they also have the pipe to attach down at the header. I think their price was also for the Power Commander and tuning.