There was a guy on here that ran an AutoZone cherry bomb glass pack on his ninja 650. Sounded like ass. Looked worse. 2 bros makes a nice pipe, but look into delkevic, I've put their full systems on bikes before, good looks, great sound and very affordable for a 100% stainless exhaust.
http://www.delkevic.us/index.php?route=product/category&path=8490_12840_12873_12878&category_string=Motorcycles %26gt%3B Kawasaki %26gt%3B 2013 %26gt%3B ER-6F ER6F Ninja 650 (2012-2016) > Complete Systems
They also make slip ons for the 650