I have the BB as well. My nitpick is that the Canon version fits the 580EX II only. I have the 430EX II and I added some velcro strips above and below the flash head to flesh it out a bit, but the BB still doesn't fit snugly, which causes droop. Unless they've come out with another version, I don't think the BB will fit the 660 EX-RT either.

Harbor Digital makes one that is more universal, but it's not collapsible, so it's not as easy to pack it along in your kit.

http://www.harbordigitaldesign.com/x...ionlens-1.aspx

There's a start up company called Magmod that looks promising. They're supposedly developing a flash extender attachment for their system. I think they show great promise.

http://magnetmod.com/