Hi Martin, welcome to the forum.
I actually had the same concern in regards to buying from overseas because of it being cheaper. What I found is that it should not matter if you buy it from overseas, the United States preferably, say from this website, which is where I got mine from:
http://www.weatherbuffs.com/SearchResul ... tage+Pro+2
Whilst it has default settings with US units, you can simply change these by following the instructions to be AUS standard. In regards to the rain gauge, it has been made for US recording of rainfall in inches, so your package should come with a little calibrator item which you can insert to make it record mm's accuratley.
It seems a little confusing at first, but if you email weather buffs with your intentions and questions (which I did), they will get back to you fairly quickly, and then hopefully your situation will be solved.
The main difference between the US and AUS versions, is with the wireless frequency's used on the wireless versions, where the US use different standards of frequncy compared to AUS, but it does not make a difference. As I said, email the people at weather buffs, they are a great help mate.
Personally I have had no problems with my station, Davis Vantage Pro 2, except if you get it, just remember to insert the calibrator in the rain gauge, I forgot to and was getting wrong readings.
Hope this helps.
