seems like it would have a better chance of working on a forearm and with two braclets instead of one with the image displayed between the two (this would fix the issue with you finger blocking the displayed image)
Only if they're smart, they're using the reflected information from the finger to detect exactly where the finger is on the 'screen'. The blocking of the light is in that case a requirement. I would imagine that a second band would be a nightmare coordinating the displays so they properly overlap. Heck, just keeping the band in place so you can display on a relatively flat surface will be more than a bit of a challenge.