I think the strongest reason against DHA purchases (I don't consider them investments) is points 3 and 5 mentioned above.
The resale market is only to other investors that are convinced its a good investment.
If you can't sell to owner occupiers, you've just removed the MAJORITY of your potential pool of people to resell to - this has a devastating effect on your ability to make any capital gain from your investment - if you're not chasing capital gain...be sure to understand why! (see article below)
The marketing people will have you believe that DHA is a great investment from a yield perspective...maybe so, I haven't crunched the numbers. But in my opinion, I would wonder - who cares?
Yield is important to ensure you can hold the property, but if there is no capital growth and you can't sell it for a profit or release some equity to buy the next investment, then you've just put a massive road block in your wealth building path.
I am at the asset accumulation phase of my investing journey, so my opinion is skewed towards capital growth investments. Unless you have a sizable equity base already, in my opinion $4-5 Million in debt free assets, then you should be looking for capital growth assets...not high yield.
This article from Your Investment Property magazine, although now dated, gives a good example to illustrate my point on why capital growth is the sensible strategy during the asset building phase of your wealth creation journey: Why capital growth is still king