As far as I know there are only two Twotters flying in Australia, Karratha Flying Services and FMG in Port Hedland.
The Pievan was a good aircraft, I beleive Fugro in Perth have one for sale VH-WGT. They are very quirky but a good solid honest aircraft for the job they do.
The -400 Twotter will certainly be the pick of the bush aircraft, Zimex have got one I know of and an operator in Nigeria has one too. So far I have not heard any negatives about them.