By default Chromebooks only allow installing apps via the Play Store, so people will only be able to install the version number sans the u.
Thank you 
I see it can be done...
however for the few blocks that I rarely use, it doesn't seem worth the effort. I may just try it one day for fun....
Which blocks are the issue? I don't think you'd be able to send/receive texts and calls on the Chromebook.
Only for development / block building purposes, I would use a real device (and probably an apk) to test sms or calling.
Pleased to report it all worked first time (companion app from Play Store). Was a bit concerned about the strange ip address that the companion displayed, but as you said above, it just negotiates a connection and works.
The Android apps run in a sandbox separate from the rest of the Chromebook software. The WebRTC functionality in the Android companion is capable of negotiating a route between them though. In the worst case it falls back to using the TURN server we run at MIT (not as ideal since all your data have to bounce across the pond).