Onyx really seems to have ticked all the boxes with the available technology. Not only is the colour contrast and saturation looking better (it still has some way to go in future) but there seems to be a lot of attention paid to the OneNote app as well as the drawing app. For functionally, too, it does what is needed for PDF annotations using a WACOM stylus. The text for actual reading looks pretty sharp for a colour eInk too as it is 300 DPI in black and white mode. Being Android based, it even has the Kindle app (with ecosystem) available to use. So as far as this size goes, Kindle is really going to have to make some dramatic changes, as it is now eating dust.
But the screen size is not ideal for typical A4 business documents or educational textbooks, so on that front if this was scaled up to a 10" that would be perfect (at a cost of course). Sadly, the 10" size eInk readers are usually quite a bit more expensive. Yes, one could use an Android or Apple tablet, but that comes with extra weight, short battery life, and are not great in the bright sunlight.
Watch the video at