Huh? This does not appear to be eInk. It's some form of reflective LCD.
It says
here "circular polarizers". That's French for "I'm not eInk".
My little clock display is a 128 x 64 yellow OLED.
The resolution is adequate to display "Wednesday" across a line (if you don't mind the jaggies).
256 x 256 does not even come in question.
As a data display if you could still see through would be useful.
I wouldn't mind having a voltmeter where you could take readings while holding two probes.
$50 would be ok for fun, $350 is ridiculous.
OTOH, head mounted displays that aren't too thick have somewhat of a future for something. Maybe.