'Slightly' OT, but if you're going to use an ISOFIX seat over here, double-check with whoever provides your CTP insurance that they'll cover medical expenses for the restrained child in the event of an accident.
I sent the following to Allianz (they provide CTP here in SA) and was told that yes, they would cover:
Cheers
Steve
p.s. While you're at it, write to your federal MP asking them to nag whoever's responsible for car seats over here to pull their finger out and have ISOFIX seats approved for use in Australia.