Oppo F1s unlocked; the Optus version sold by the Optus online store is locked and also has network bands optimised for Optus; this one is uncrippled for networks.
Oppo's price is $348, but $338 with a $100 voucher is a decent deal.
Note that the Australian model of the F1s is not dual-SIM. It has one SIM slot (nano-SIM) and one microSD slot.
This model does support B28 (local AU stock).
The Optus prepaid model does not support Band 5 (850MHz) 4G for Vodafone, and 850MHz 3G for Telstra/Vodafone, this is a slightly different handset from that sold by Optus.
Pretty good deal, when Optus sells it at $339 unlocked ($259.00 + 80.00 for unlock). Might as well get a voucher with it.
It's a really good phone