We had ducted heating installed by Air Plus Pty Ltd. While the system works alright (with the exception of being too complicated to program, and we're both fully qualified scientists!), we are very disappointed with the service provided. There were four main problems. The installer: 1) didn't ask where we wanted the control panel mounted, and as such it is now located in the middle of our hallway wall in an awkward and unsightly position; 2) cut right through a large beam under the house to install a vent after he'd accidentally cut a hole in the floor of our dining room without checking the location's suitability for a vent; 3) didn't run the remaining vent to our bathroom as we'd asked him to (we said to just leave this one under the bathroom floor because we needed to renovate the bathroom, but have now discovered that he didn't even run the ducting to this location); 4) wasn't terribly friendly.
Overall, based on our own experience, we wouldn't personally recommend that anyone go through this lot for heating and/or cooling.

Approximate cost: $>$2000K