A quick look at the measurements reveals that this generic board is roughly 2 1/2 inches narrower than Nintendo's board and almost an inch shallower front to back. I can't speak for everyone here, but my size 12s are already poking their way off Nintendo's board. I can't imagine using an even more cramped peripheral for Wii Fit.
But should you be a Lilliputian, you may benefit from the electric blue non-slip surface. Like Lam. That guy might love this thing. (I squish your head, Brian Lam. I squi- OK, please don't fire me...I swear your head will be fine with a little rehab.) [Chinavasion via CrunchGear]