As far as I know and have seen, all E-Ink panels are fragile and can get damaged pretty easily by getting hit, being left in a very hot/cold environment, having put under heavy stuff, and other kinds of accidents that might cause direct damage to the screen (other electronic parts are not as fragile as the screen on any of these such devices and although E-Ink panels might be more fragile than LCD ones, but LCDs and other technologies break too!). That is why a hard case and maybe a small tablet bag are necessary for these devices IMO.
All E-Ink panels are made by the same company (
E-Ink) using the same production lines; so I don't think any of the members of the same model of E-Ink panels are of higher/inferior quality compared to others.