This deal is from the Coles catalogue starting Wednesday 18 December.
IMHO there are 2 great options for using this starter pack. Either way, before you activate make sure you get a promo code from a friend already with Belong for an additional $20 credit.
Option 1 - start out on the $10/month plan. The first 6 months cost is already covered ($40 starter pack credit plus $20 referral credit). This is a good option for those with modest data requirements (average 1GB/month).
Option 2 - start out on the $40/month plan. When the first billing day comes you'll already have 80GB data (minus what you already used). Then switch to the $10/month plan. The first 3 months cost is already covered, and you'll have nearly 80GB banked which never expires and can be used or gifted.
Update for Option 2: If you are activating before 31 December there is this alternative to using a promo code from a friend: https://www.ozbargain.com.au/node/501982
If you are porting your number to Belong then this gives you $50 credit, which you could use to stay on the $40 plan for an additional month and get an additional 40GB (total 120GB), or you could use it for several more free months on the $10 plan.
BTW this starter pack may still be available at Woolworths for the same price.