A wise man once said that there's no better problem than a tax problem :)

Member Rewards will have tax implications. From their website:

Any earnings on your investments are subject to taxes according to Australian tax laws. After the end of each financial year, we will send you a single annual tax statement by email known as an Attribution Managed Trust Member Annual (AMMA) statement. Before the end of the financial year we will also ask you to provide us with your TFN, so that we can pre-populate your gains and losses to the ATO.