From the Twelve South page:
Now milled from aluminum, BookArc features a bead-blasted finish. A polished chamfered edge pays homage to the new mirrored Apple logo featured on the new 12-inch MacBook. Finally, the entire stand has been scaled, refined and optimized to fit every current MacBook, from 11-inch Air to 15-inch Pro with Retina display, with one BookArc.
I have the older one I bought for a rMBP 13. It really is a high quality product. I am most likely going to buy the new one to go with my new rMB 12.