1. Custom file system: this means I can ssh into it, but I can't rsync my bibliography into it, since it won't display regular pdf files whose name is not hashed and registered in some sort of index. Moreover, the lack of a Linux client meant it was very hard to put my pdfs on it, or extract my notes from it.
2. Left hand support is ridiculous. They just flip the screen left-to-right; which means you lose the nice bevel and it becomes very uncomfortable to use in "handheld" mode. Finally, the "close" button gets placed on the top-left corner of the screen, which is the first place a left-handed writer touches.
3. The lack of some sort of backlight and slightly gray background means I can't read under suboptimal light. Sure, I get it, its e-ink; but for the price they charge, it would be a very nice-to-have feature.
I ended up returning mine and went for the Samsung Galaxy Tab s7 and that thing is amazing! Plus, I get to follow through bibliography immediately without needing to go back to my computer and get another article then do the whole sync'ing dance again.