[otnt]

 The new Boox e-ink is about 1.3 lbs.  Using a weight limit as a primary concern, you will probably have to look at the 7-9 inch phones/readers/tablets and consider their ability to page/scroll and annotate, along being able to read the charts.

Sony's Digital Paper are:
10.3" is 240grams/0.53 lbs
13.3" is 349grams/0.77 lbs

One can annotate PDFs very easily. But Android is not natively accessible on Sony's Digital Paper.

Unfortunately to access Android these need to be rooted and to get Bluetooth working (wireless page turning) is even more complicated.

Onyx is loosing on hardware side and Sony on software side.