Win,
Apologies for the delay in responding - I must have missed your post in my feed of 'latest posts'.
I don't think a centre mount would be an issue legally. Being offset gives a better rear view. For some purposes being hinged on the drivers side would have been better for me, but then the carrier would swing into the traffic lane if parallel parked on a road.
I crossed the Simpson, and done some rough tracks, including some in the Victorian High Country, and didn't have any issue with the 'unbalanced weight'. It has a very secure mounting system, and has caused me no issues. I only use it on trips when I want to carry a second spare, and store it at home for regular driving.
Greg