both the Sennheiser and the Shure PSM 300 wont run well in all parts of Australia. At current there are no affordable digital IEM's that don't run on the UHF band which is congested with Digital TV and 4G.
Not to mention that different frequencies are taken up by Digital TV in every state and territory so you need to find out if you can legally run IEMs with out interfering with any other transmission before you vote and buy.