I actually have the smaller 430 Carbon, but the same Roller 2.1 mount. It's a great bag, and the mount is awfully nice, both when using the bag, but also for easily transferring between bikes if you get an extra mount. The bag includes two integrated tire levers as well, which cleverly stow on both sides of the bag's top piece.

I got mine from Nonstopciclismo's eBay store: SCICON ROLLER 2.1 SYSTEM SADDLE BAG ATTACHMENT CLAMP items in nonstop ciclismo store on eBay!