I don't really like it. Aesthetically, it's slick. But I don't think that form factor would work. I think the controller would be much more comfortable and lighter if the screen was on top of a standard controller. So when you are holding it, it feels like a normal controller but looks like an iPad in portrait mode. So it would still be a flat surface on the front, but taller rather than wider.
That way, when I hold the controller with one hand, it doesn't feel unbalanced and I can easily manipulate the touch screen with the other hand.
I know what your thinking, this mock up allows you to access the touchscreen with your thumbs, but I don't think that's possible. Not with the added width two joysticks, a d-pad, and buttons add. So it all comes back to how comfortable can I make the device when holding it one handed.
Go ahead and try it out. Grab a book and hold it in one hand in portrait and landscape. You'll see my point.