Its a safe n sound maxi rider, AU and NZ standards
from memory it was NZ from MEL to CHC, but not CHC to MEL that I was able to take it into the cabin.
JQ and QF (when they operated the route) were a no-no, I will be test driving DJ in November.
Derab, that's strange that Jetstar would not allow your car seat onboard.
I personally fitted a car seat for a family last week on a CNS-MEL flight who were pre-boarded (prior to general boarding) and there was no issue. So long as the car seat conforms to Australian standards then we allow it - we even have our own blue restraint straps that attach the car seat to the passenger seat, and obviously the passenger seatbelt passes through the rigid frame of the car seat.
My only theory is maybe the Christchurch-based Jetconnect/Jetstar crew were being lazy or haven't been trained to fit the car seats? I really don't know why they didn't allow it.