Dasung is also producing a 13" device.
http://goodereader.com/blog/electron...-paper-monitor
They are aware of the potential of the device as a secondary monitor and focusing on it. They are doing it via Bluetooth. Onyx are also doing it. This IMO is a big flaw in the indiegoreader: no bluetooth.
It seems connecting as a secondary monitor is difficult to do, and Bluetooth is the simplest option.
Interestingly, though Boyue has no Bluetooth, they support USB OTG. I don't know if that means it could be used as a monitor. But they only do 6" devices anyway, so don't seem interested in bigger formats.