[Matt Devo]

Loading ChromeOS
With 2 different USB memory keys and an SD card I did not manage to have CN60 ChromeOs recognise there is an O/S on the memory device upon insertion.
 

Recovery Mode is just picky about USB media and port used, that's all there is to it.

 

The next day back to EZ script
As per your reply, this time I managed to download LibreElec after selecting 2 for dual boot update:
LibreElec download complete: installing...
cp: error writing '/tmp/System/SYSTEM': No space left on device.

Please can you confirm what this means? My understanding is my partitions may be too small so I have to:
1. Perform a factory reset (I'll have to try again, any tips?);
2. Reinstall EZ script and run it again (is there another way?). 

  
the error means what it says, not enough room for ChromeOS to download/extract the LibreELEC image before copying to the partitions set up for it. Whatever value you used for the LibreELEC partition last time, go 2GB less this time. You will have to do a factory reset (to reset the partitions to stock) and then re-run the EZ-setup script (resize them). I'm baffled as to why you are having some much trouble with this.