I can give you an insight to the credibility of Deakin as an institute of Higher Education, but will leave the specific analysis of MBA programmes to someone else.
As a university lecturer, I can tell you that Deakin is generally perceived as a solid mid-tier university in and outside of Australia. Perhaps comparable to the UK's Universities of East Anglia, Essex and Sussex; that is to say, generally good but not world class in most areas.
6k for some intellectual stimulation still sounds good but if the prestige is an influencing factor, it might be worth checking if there are other 'more reputable' places before handing over your well earned cash.
Very best of luck my friend!