Ok everything is now working sorry spotted that the USB device disappears because it then reports to be an Arduino Leonardo … After flashing my 1st program it reports to be a Xadow 
Also spotted that the installation includes the files to be dropped into the Arduino\hardware\seeeduino folder so that the board becomes supported.
May be time to alter the WiKi so that people don’t get confused by the instructions.
Cheers,
Mike