For the first minute I also thought this was an early/late April Fool's joke, but I can see this working. Especially since it has a battery and doesn't rely on a power outlet. Three hours of batter life seem not that much though and should be improved upon.
On the other hand, most if not all newly released BEVs support a regular power outlet so you could also bring your 55" 4K TV - if it fits in your car AND is well protected. This screen solves both potential issues, with its own caveats of course.
I like or rather LOVE the idea, but not for this price.