If you got an MK2 / MK3, good for you...
As for all the others (like me) with an MK1, being forced to use another solution (like Supercard), it is not a nice situation to be out of any support.
Nevertheless, I tested Tetris DS and Metroid Prime Hunters, in NDS mode with GST 3.1
Tetris locks at a black screen.
MPH gets to the "ESRB Notice: Gameplay experience could change during online play", and gets stuck there.