I bought an ASUS ZenScreen for my mobile computing kit. I had intended for it to connect to my Google Pixel Slate but then it failed to connect out of the box. (more later) I tried to connect the display to my Chromebook Pixel and it worked So I was encouraged.
This morning I decided to connect the ZenScreen to my ASUS Chromebox as my 3rd monitor and it works great!
Back to the Slate. What I have read is that the problem may be in the OS or maybe the firmware related power management. Some people have had success using power hubs but none have described why, only the model(s) that worked. After my reading of product descriptions I got the sense that it is probably PD. Which is the ability for power to be negotiated and multi directional. And so that is the next test. Not all vendors properly describe their products.
In the meantime the ZenScreen is a nice addition.
PS: the ZenScreen got an expensive update this year. They added a battery so that Android devices, including phones, will work too. This means adding a Bluetooth keyboard and you have an all in one solution, sort of.