Our experience was with a hired child capsule mostly used in a MINI Cooper S. Both my wife and I are fairly short (5'6"), so we had no problem putting our baby into and out of the car, while still letting him sleep in the carrier. It even fit behind the passenger seat (just!). Of course, we didn't have a pram that the carrier would slot straight into, but it was no problem for us to carry him with the carrier handles.
All Euro cars sold in Australia are designed to take either ISOfix or ADR compliant top-mounts. However, as far as I'm aware, only Australian Standard restraints are legally available for sale in Australia (thanks for clarifying Duncan). OK, no problem with importing an ISOfix restraint if you don't ever have a crash. But I can't help but wonder what would happen from a legal perspective (let alone the personal tragedy), if you were to have a crash and the use of a non-ADR compliant restraint was found to be a contributing factor in injury to your child. It's not a nice thing to think about, but as a parent, these are the sorts of decisions you need to make.
From my perspective, the ISOfix system has it's limitations. Since it's physically latched to the seat base, the restraint will not move in the event of a crash. Hence the only thing restraining the child is the harness and all the load will be distributed on those thin straps. This is less of an issue with rear-facing restraints. On the other hand, some research suggests that ISOfix offers better protection in side impacts.
The advantage of the ADR-compliant restraints is that the top mount allows the seat-base to rotate forward slightly in a frontal collision, before the seatbelt catches the back of it. This means that the restraint and the harness both combine to slow down the child's movement, spreading the load over a much greater area and cushioning the impact. This suggests there should be a lower risk of injury with ADR restraints compared with ISOfix in frontal impacts. The downside is that the ADR restraints can twist in side impacts and offer a bit less protection than ISOfix.
The critical thing to remember however, is that both systems must be properly fitted everytime they're used. So ease of installation should be something you consider.
If you chose to go with a cheaper and ADR-compliant restraint, then some great advice on selecting a baby or child restraint is available at the following links:
http://www.atsb.gov.au/pdfs/child_restraints.pdf
http://www.mynrma.com.au/cps/rde/xch...restraints.htm
http://www.racv.com.au/wps/wcm/resou...t%20Report.pdf
A detailed comparison study of ISOfix, LATCH and ADR restraints is available here:
http://www-nrd.nhtsa.dot.gov/pdf/nrd.../07-0298-O.pdf