I am using the "Europe/Asia" Electron with Sara U270 modem (900MHz/2100MHz) in Australia. It works very marginally with the Particle SIM, as that SIM uses the Telstra network, and the only band the U270 can use with Telstra is 2100MHz. Unfortunately, most Telstra 3G is provisioned using 850MHz, which is not supported by the U270.
As my application is mainly driven by SMS, I have simply put in a Vodafone SIM and it works very well. I am testing with a $10 prepaid Vodaphone SIM (365 days, 2c/MB data), and I've noticed it's never charged for data - so far - maybe because particle IO never gets over the minimum session threshold.
However, if you want to use the data-only Particle SIM, then I strongly advise getting the "Australia/USA" Electron with the U260 modem (850MHz/1900MHz). While this can still only work on the 850MHz band (no carrier in Australia uses 1900MHz), this is the better provisioned band for Telstra.
It's really unfortunate that Particle chose not to use the Sara U201 version, which covers all 3G bands world-wide, and would work better in Australia both with Telstra (3G 850 and 2100) and Vodafone/Optus (3G 900 and 2100). At bulk, wholesale prices, it would only have cost them another 10-15US/chip. I'd've paid a premium for that version!