The main issue I have with them is if you are selected for them, you are forced to go through it or you don't fly (with limited exceptions). A complete reversal of what was promised during the public consultation before they were rolled out and completely ignoring what both House and Senate committees said in their reports and every single public comment about them.
I contacted DIT about them a few months ago. They tried to fob me off and only cut/paste text from their website on the topic. After making it clear to them that I was not to be treated like a fool, they told me to go ask the airports. SYD replied, MEL didn't.
Thus far, since their roll out in Australia, I've been lucky enough to avoid them (even yesterday in SYD when it wasn't in use and I was the only one in a batch of 5 to be sent through the WTMD). A few weeks ago in MEL, the scanner was having issues and everyone was sent through the WTMD until the MMW was fixed.
If they select you, you just say "I am medically unable to assume and hold the required position".
I have no issues with the ETD swabs. That's doing something useful. MMW isn't.