My experience talking to pilots who have gotten these medicals is that due to the extra CASA stuff on top of the "Drivers Medical" and the fact that the doctors are a bit cautious is that this medical is essentially the same as a class 2 medical. The only difference is that any GP can do it. It also apparently costs around the same as well.
I guess you are aware you can only carry one passenger once you get it.
So the advantage seems to be that any doctor can do it but the disadvantage seems to be that it is about the same as a Class 2 anyway with passenger limitations.
Also it seems that if CASA has ever refused a medical for you or asked questions they will not issue this medical to you anyway. I know one pilot who got it (it comes instantly) only to get a registered letter a week later telling him it was not valid. Said pilot went on with the usual hassles and eventually ended up with a Class 2.
Sorry I am miles from Sydney and can't actually help with a doctor.