That's not the point. The GP comment clearly referred to using the second screen to share with someone nearby, such that two grown adults don't have to huddle around a single screen, possibly sharing earbuds. If you know where someone lives, why have a phone when you can send them a letter, right?

The point is, if you have two screens on your device, it would be useful to be able to unhinge one (possibly still tethered) to make it more convenient and comfortable for a second person to view what's on your device.

I would absolutely buy something like that for doing in person usability testing with prototypes in settings outside a usability lab.

This sounds like a solution for software rather than hardware. Everyone has a smartphone. I would rather not have others handling my devices.

>I would absolutely buy something like that for doing in person usability testing with prototypes in settings outside a usability lab.

This sounds like an extremely niche use case.