[1] https://www.movidius.com/solutions/vision-processing-unit
[1] https://www.movidius.com/solutions/vision-processing-unit
For one thing, this board in particular apparently has a direct connection to the camera. I'm not sure if you can do anything but live video from the directly-connected camera (in my case, I want prerecorded video / video from IP cameras). Maybe it can but it's not immediately obvious anyway.
The $75 "Movidius Neural Compute Stick" uses the same chip and does everything via USB so that's more promising. But it's a binary-only API that's totally focused on neural networks (and only available for Ubuntu/x86_64 and Raspbian/arm7). In contrast, I believe you can easily send Hexagon arbitrary code. Its assembly format is documented and upstream llvm appears to support it. So if I want to do background subtraction via more old-school approaches, the Hexagon is probably useful where the Movidius stuff is not. And I have yet to learn anything about neural networks so that's a significant factor for me at least.
Really neat hardware but I wish it were more open.