So I might have gotten hyped too quickly. The previous pictures were of optimized apps; the Kindle on the Duo looks great. I heard unoptimized apps that try to span across the two displays were wonky but I thought that was just the controls. Once you started reading how bad could it be, right? Here's a screen grab from MrMobile's review:
Instead of half of the content shown on each side of the screen, unoptimized apps see one whole screen and content is missing in the middle where the hinge is. Microsoft presents the hinge space as part of the screen
So I do have to wait for every pdf/comic/manga app to update with span support...