If you go to the nemoptic website you can look at some of the detailed specs for their current evaluation products.
Good: They promise "Image Change no flashing effect, no image
persistence". And "Response Time <0.25sec/image at Room Temp", which is a nice step.
Bad: "Image Mode B&W (1bit gray scale)" and "(145dpi, sub QVGA)". I guess it is just black or white.
Oh well, hopefully more manufacturers lead to more products lead to more competition lead to much better devices.
Until then, I will stick with my prs-500.