I have installed without a db killer. I don't think it is too loud as it is but I do not have any ride time as unfortunately it is snowing here today. I will update if I change my mind and put the db killer in.
The good: - sounds a lot better... it's a nice deep tone that is noticeably louder than stock. The crap cell phone video doesn't quite do it justice. - dropped a fair amount of weight - looks good, better than stock in my opinion
The not so good: - fitment isn't perfect; the opening that slides onto the stock pipe is a little too small. As you can see in the photo, I wasn't able to get it all the way down to button up properly. It's on far enough to clamp down... If I could stretch it just a little, it would be better; I'm sure there is a way to accomplish this, I am just not sure how.
Video uploads failed... I'll try to figure out how to get them up.