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And the 640 x 48 resolution is fine for glancing at and poking and swiping from a few feet away. But get any closer and things look pretty grainy.
The pixel density might not be that much of a concern in practice, since it's mounted on a keyboard, so you typically wouldn't be viewing the display up close. 640x48 on a 5" screen works out to be a similar pixel density as 1080p on a 17" screen, or 1440p on a 23" screen, and most desktop monitors will have lower density than that.

Though for $100, it seems like they could afford to make the screen a little larger, as the viewable area is only about a centimeter tall. Maybe increasing the vertical resolution to 64 pixels and the height by around 33% could make it a little easier to view. And give it a better panel type. It's possible to buy a 24" 1080p IPS monitor for $100 now, so surely there's a decent amount of room to do better with a panel less than 1% the size. Perhaps they are limited to existing touch displays though, as making a custom display might not be practical for a niche device like this.