No one holds a controller where that layout makes sense, you'd have to have the tip of your thumb resting in between A and B in a game like SMB, trying to keep B pressed with one edge of your thumb, and using the other edge of your thumb to hit the action button.
My way makes much more sense, and is the way Nintendo and 3rd parties handled it when moving to the SuperNes and its control layout, which this thing replicates. Everyone did it my way with ports of NES titles and SuperNes entries of 8 bit series, including titles like Super Mario All-Stars. The functions mapped to B on a NES controller typically became Y on a SuperNes pad, with the functions mapped to A typically going B on a SuperNes controller. That way, the tip of your thumb can keep B (Y on a SuperNes controller) pressed, while the portion of your thumb closer to your knuckle can handle hitting A (B on a SuperNes controller).
I think this is obvious and several agreed and provided their own diagrams showing the exact same thing (SonicWolf's), though apparantly next to no one bothered to actually click on my attachment and see what my thoughts were. So I hope its taken into consideration.