Re: Multiple screens?
In the case of my Asus Chromebook Flip, it can not only drive an external HDMI display, but the default in Chrome OS is to treat it as a separate "screen". When I have worked from home, I link the Chromebook to a 1080p display and run Citrix Receiver on that, with the Flip's own screen (1280x800) kept for anything running locally.
(On a side-note: Chromebooks have come on a long way in the last couple of years, but from the kind of criticisms that keep being raised about CBs - "they can't run multiple displays"*, "they can't print locally"**, "where are the apps?"***, etc. - you'd think Google had frozen development some time in 2013...)
* - They can (see above)
** - Local printing support was added in 2016
*** - Android support in COS is now pretty good, and Linux "container" support is on the way