For those travelling over that take out travel insurance with Multi Trip...
You are not eligible for Medicare while in Aus. The company will tell you that you must "enrol" with Medicare if you find yourself needing medical treatment. They have wording in your policy stating the same. However, you are only entitled to to limited subsidised health services for medically necessary treatment while visiting Australia. You cannot "enrol" with Medicare while in Aus and you will not have access to the benefits that Medicare offers.
You can present at a hospital with your passport and you will get treatment based on the reciprocal healthcare agreement between Aus and Ireland which is the same as having a medical card back at home.
As this insurance does not cover you for non-emergency medical situations it is essentially useless for travelling to Aus. You will not be entitled to any refund on visits to GPs, specialists or scans/x-rays that may result in you having to attend a hospital for further examination.