YES, using a VPN is 100% LEGAL in Australia. You have the absolute right to online privacy.
BUT... doing illegal things using a VPN is still illegal. (e.g., downloading copyrighted content via PirateBay). A VPN protects your privacy, not illegal acts.
What about Netflix? Using a VPN to watch other countries' Netflix isn't illegal, but it does go against their Terms of Service. A distinct amber/orange glow means caution.
What is the best VPN for Australia" to stay safe legally? Paid VPNs offer better legal protection and anonymity than free ones. Choose No-Logs.