I wasn't willing to pay what Yamaha wanted so I picked up the detachable Sissybar/Backrest/Luggage rack combo from Cavalry Fibreglass:
It seems solid with a large back pad, and its TALL (I had a Cobra short backrest before.) Quality of the luggage rack is below the Cobra, but the shape is a lot cooler. Overall quality isn't up to factory, but it's also 1/3 the price. The pictures show it with some wierd reflector on the back of the seat, but mine came with a decently cool looking Iron Cross shape.
I should be getting the bike back together in the next few days so I can review the fitment, etc. when I do.
**EDIT: I just looked at your post and the link, and the pictures on your page are identical to the ones on Cavalry. So I guess its down to price if you like that one. I was never able to find any other detachable other than this and Yamaha's.