Pros:
-Possible power gain
-No second cat to deal with
Cons:
-Possible power loss
-Costs time/money to fabricate
-Noise level may get you pulled over
-Go riceracer go!
I ran without the backbox once, was hilarious but really loud.
Sound is out of sync a little and it's only my go pro but here:
http://s221.photobucket.com/user/canablist/media/MyMovie.mp4.html