Joe @ Zpacks.com is a great dude. He has helped me with custom gear before, and to this day I have had a few hundred miles put on his cuben "Blast" backpack that he made in a smaller size and sold to me. The cuben he used on the pack is about 1oz/yard. Read: strong
I have done dozens and dozens of miles of backpacking through catsclaw and shrub live oak with very little fraying (and only to the outside pockets)
so if he is charging a fair amount for a tarp (which he pro'lly is) Id say go for it.
The problem of durability in Cuben is when you start trying to make gear from the .44 or .33 stuff. As explained to me by Ron Bell of MLD, the .6, .7, and 1.0 is perfect for gear. Just hope tree branches dont fall on ya.