I went to the site - it looks like you got the Alvin 4x8 mat?
If so - Alvin mats are great. I bought one, then got a bigger table and bought another larger one. I'm very happy with it!
I've never used a Martelli mat, but I own Olfa, Fiskar, Dritz, Omingrid, and Alvin brand mats and I like my Alvins the best.
That is going to be one awesomely large cutting space! I hope you'll post pics when it's done!