Success!
In desperation I thought i would try it (reading literature it seems the silicon inserts stop milk getting into the machine, so you have to clean it - worth the risk). And when I looked at the accessories page there didn't seem to be many difference between goats and mares other than the silicon insert and size of glass jar.
It even worked on goat that wouldn't 'let down', she was rock hard on one udder that hadn't been milked for 2 days (not for lack of trying as I was with her for 2 hours last night). So despite saying hand milk to get milk flowing it did the whole job on a very nervous, tense goat.
Fab, fab product (thx jakay!). So great in fact my miserly husband says get another one so can milk two udders at a time and have a back up if one needs repair.
John at Udderlyez also emailed back after I had milked the goats to say, yes can use mares one on a goat (phew), but he will email fully on Monday, so will update re any additional items to buy. Great support for a weekend.