I have both the small and large Brooklyn Revolvers - While they're a bit smaller, I like them better because the turning mechanism is much smoother.
I also have a 24" square one that a friend made. Comes in handy for squaring larger blocks..
Either brand, they're a great notion to have.
Here's the Connecting Threads page:
http://www.connectingthreads.com/Olf...lfaRotMat.html
Brooklyn Revolver (also pricey):
http://www.comequiltwithme.com/shop/...roducts_id=174