XFlex bonus is the extra goodies you can purchase directly from http://www.skinsforsale.com - We don't mind if you buy from here or snowcovered, especially if you want to use your developer discount, but, if there's no savings for you, or you want to get exclusive things that aren't listed anywhere else for sale, then you can purchase XFlexBonus with extra containers for your website.
It's the XFlex Platinum with some extra containers show here.