The Buddha Board looks like a useful tool to practice things on, but I think that's a bit deceptive.
Part of practicing is comparing your works with each other to notice progress and find repetitive flaws, and since Buddha Boards works vanish after a while, you'll never really be able to tell the difference! Seems a bit counter intuitive to me.
I think pen and paper, or saving every drawing on your computer if you work digitally, is the best way for gesture drawing. The Buddha Board looks like something to use when you need to sit back, doodle something and relax without worrying about the lasting effect of your drawing. :)