Thanks for getting back to us and letting us know what ASUS says, I’m happy to add more information.
Both the docks I listed are compatible with ChromeOS, and to be sure, before I sent you the recommendation today I did test the UD-ULTC4K with a Samsung Chrome Book we have in the office and everything worked as expected including my three external monitors.
The second and third monitors on the triple display dock (UD-ULTC4K) and both monitors on the UD-6950 dock are powered by DisplayLink software which is already built in to ChromeOS. So, while your Chrome Book only supports one external monitor via the USB-C port, the DisplayLink chips in our docks will drive the other monitors using the DisplayLink software.
I hope this added information helps, and we do have a 30-day no-hassle return policy so if your Plugable devices do not work as expected we will happily issue you a full refund if you’d like to return the device. Please let us know if you have any questions about this or if we can provide any further information. We are always happy to help.