Looks a bit better in person than in the video.  The thumbs are pretty small, and the wrapping isn't ideal (might be better wrapped to columns?), but it does give a nice "map" of the book.  You know exactly where you are, both within the chapter and within the book.  And jumping anywhere (including to the beginning of any chapter) is really easy and feels good.

(By the way, the weird vertical black line near the right side is due to a hanging string that's blocking the projector, which is holding up the Maxwell hanging-mobile-diorama thing.)