There are many threads on SPOT, PLB, and satellite Pros and Cons here on BPL. You need to identify what is important to you and your hike.
I hike solo on the JMT, the Winds in Wyoming, the CDT in Colorado, and the Grand Canyon. Trips are typically 7 to 10 days long. Off-trail routes are common. Camps are out of sight and sound of trails, when possible.
I have a 3 year old McMurdo FastFind 210. $250US at REI and many other places. Weight is 155 grams. Battery life is 5 years. You will need to register the unit with NOAA. It's free, easy, and instant. My unit sends only "Come and get me." No texting. No "I'm OK."
When activated it sends a GPS location to a government facility which then notifies the relevant county sheriff. (In additon, it broadcasts a local homing signal to help the "near in" search.) The sheriff then coordinates the S&R. The contact information you provide is to confirm the signal is not a false alarm (amazingly common). The S&R will proceed whether or not communications are established with your contact information.
You could probably sell it at the end of your trip to recover half or more. You would have to re-register the unit for the new owner, who would then gain total control.
If you want basic and bombproof this, or whatever is current, is my recommendation.
Edit: If you can convince yourself of SPOT's reliability, it offers $50,000US of S&R insurance for $13US. If this appeals to you, check to see if SPOT and its features are supported in Australia.