If you can't churn onto Superloop's gigabit deal, this looks like the next best offer as far as I can see. Ends up being about $70.67 p/m over 6 months. Compare that to Superloop's gigabit $89 plan and with their $105 cashback, optus beats it by about half a dollar.
But If you can include a referral Superloop ends up better.
Plus $170 cashback @ TopCashback - https://www.ozbargain.com.au/node/877771
Optus Typical Evening Speed 780/40Mbps.
Supply your own router or..
Pay $0 for our Ultra WiFi Modem Gen 2 when you stay connected for 36 months (normally $306). That's a $8.50/mth discount on the modem for each month you stay connected. If you cancel before 36 months, you'll need to pay out any remaining cost of the modem, e.g. if you cancelled with 12 months remaining, you'd need to pay $102 ($8.50/mth x 12 months remaining).
Cashback is great when it works