I have not used this unit but i have used a similar one. The idea is that it is kept within the tank and keeps the salt water at the right temp.
The problem is if you have a lot of younf fry it will not hatch enough of them per go.
becuase you live in sydney the temp at the moment should be ok to hatch artemia.
Save some money and use an upside coke bottle.
you will be able to hatch more and it will cost the same price as a bottle of coke!