Yep, have called Giles already.

He tells me that he paid a bit less than I was quoted, but still double the Windscreens O'Brien price. When getting prices I asked the service guy about Aussie made v OEM and I said "You'll obviously tell me to get the OEM glass, can you tell me why?".
He replied "No not necessarily. We've seen a few cars with after market screens and there does not appear to be any problems."
Giles dod mention that the OEM glass was a few kgs lighter than the aftermarket screen he was looking at and that given his was through his leasing arrangement he was happy to go that way. I think O'Briens are the winner for this little MINI driver though.