I found out the hard way having bought a faulty unit from the US. After postage to me and then return to the US for warranty and then getting it back I paid a lot more than buying it here. I also didn't have it for as month and also lost that subscription time that i had paid for. You also don't get Australian support for use and will have to contact the US for help.
The only other issue besides the expense of having to send back for warranty is that they do not have the Australian C Tick approval for use here. That technically makes them an illegal tranmitting device and leaves the user / importer open to potential fines and prosecution. More info at
http://www.acma.gov.au/WEB/STANDARD/pc=PC_1756 about the C Tick . The authorised Australian distributor for the SPOT units is
www.piplus.com.au which can answer more questions and supply approved devices for use in Australia.