The last time that I pushed into the Matrox web-site I found that the uMBP was not supported at higher resolutions. I own the Matrox DualHead2Go, Digital Edition and it worked great on the "classic MBP's" that have the full size DVI port. My experience was the the 2.4 SR version MBPs and I ran two Dell 20" LCDs at 3200 x 16; it was great.
However I found to my dismay that the MDP on the uMBP's do not work with the device. Later after the uMBP's were on the street, I found this support information (of lack of support) buried on the Matrox support web site.
I found and use a EVGA UV Plus+ | Model: UV16, USB to DVI adapter to drive my second external screen. So I work with my 17" uMBP open (1920 x 1200) and two Dells at 1600 x 1200.
Neil