Another online retailer (that shan't be named) claims that they exclusively carry the BBK Varitune Mustang Axle-Back kits. Here's the Merriam-Webster Dictionary definition of "exclusive":
ex·clu·sive \iks-ˈklü-siv, -ziv\
b : limiting or limited to possession, control, or use by a single individual or group.
In other words, BBK's Varitune Axle-Back Exhaust kits for the 2005 to 2014 Mustang GTs are now available here at Stage 3 (and are definitely not exclusive, by any means), and they're the perfect way to dial in your Mustang's sound with their adjustable volume design.