It isn’t “all or none”. There are subtleties in what the app actually is and does. It shouldn’t need to be “here is the one and only app, take it or leave it”.
If it is so important that everyone gets on board this one time then … for once in its miserable little life the Australian government could take seriously the privacy and security concerns that have been expressed time and time again, and ignored time and time again, in the past.
Since, apparently, the app is not available yet, why are they not using the time wisely to address the genuine concerns that people have?
I already gave a quick summary at the bottom of Secrecy, privacy, security, intrusion - #240 by phb above.
This is the one thing that governments have been really successful at over the last 20 years. 
Only really effective though if a substantial fraction of everyone else installs the app.
