For new readers to this thread, it's worth trying to spell this out.
The only way to avoid getting clobbered with a 3% charge for "changing currency" is to load your QantasCash card with AUD and spend it in AUD.
If you do anything else (like loading AUD and then going overseas and spending say USD) you will be charged the 3%.
So, for those of us fortunate enough to travel with a credit card, you are better off using one that doesn't charge for foreign exchange.
A couple of examples are the 28 degrees card and Bankwest Platinum - but there are others.
If you want to lock into an exchange rate before travelling, you could use the QantasCash card to buy (eg) USD and then spend USD when you purchase overseas, but you would need to load it from a bank account that uses USD in the first place to avoid the 3% charge.
However, it might still be worth taking the 3% "hit" if you are the type that wants to lock in a currency ahead of time.
As far as FFPs are concerned, the 2P/1$ offered by QantasCash might seem worth it, but again there are better deals out there.
Example, the Qantas AMEX card that gives 1P/1$ and has no annual fee (it's not a good card to use on foreign currencies, but for AUD domestic purchases it's great).
There are other cards (that have annual fees) that give you more points/$ - so shop around and find one.
For me (as someone fortunate enough to be able to get a c/card) I cannot see any merit in the QantasCash card.
For foreign exchange and for gathering FFPs there are better deals everywhere I look.