Obviously not a good value in any regular sense, but running this off a USB port and nothing else...that's cool. This largely takes the laptop's screen and makes it a separate device, so we're looking at a much more modular computer. And don't diss this for "the resolution sux"...I suspect this is a hardware limitation, but if not, hey, these will get better.
Since it's just USB, you've got much more hardware flexibility. What's got the stronger hardware...a Celeron-based Chromebox, or a tablet? If you don't like Android, the Celeron version of a Cubi, running Ubuntu.
You're right that tablets are one side of the competition; laptops are of course the other. These may not work that well until there's something in a NUC-like form factor running on battery power. Still, I think there's potential here.
Get it a battery, touch and a wireless connectivity and you can see how practical it would be for engineers and laboratories. Instead of having a low power device while working on the go, they can have all the heavy work done in some computer out of sight, while maintaining the portability.
This is a really cool second monitor for a laptop, but why don't they just also add an HDMI port. That would up the usefulness immensely. It could be powered by a USB battery pack and display a raspberry pi, or a game console, or any laptop with a HDMI port, no need for extra software. Many things have USB ports and HDMI ports, but only PC's can run displaylink software.
This device uses Displaylink Technology, which essentially compresses the video, sends it along the usb port, and the monitor de-compresses the video, and forms the display. Displaylink needs an active program that you load into your hd/ssd, and at the moment software only exists for Windows and Mac OS. So any thoughts of Ubuntu or Chromebox need to be dismissed.