@Flyfrequently I’m not sure what you are referring to when you ask if it is “easy/cost beneficial to proceed with this?”.
If it is the upgrade from another Amex card to this one - I have not done that.
If it is using the credit, then I have done that many times.
The travel using the credit is booked on the Amex Travel website (not on the QF website) and it must be Qantas flights to use the credit.
Sometimes Amex Travel will not have access to some of the cheap fare buckets that might otherwise display on the QF website as Amex have possibly run out of what they have access to in that bucket. But that is a genuinely rare occurrence for me. I have mostly seen that when trying to book something that is departing in the next week or so. Book far enough in advance and you should see matched pricing between the two websites.
The Amex Travel booking engine doesn’t know that you are going to use the flight credit when you do the search (the payment option comes later in the process) so it isn’t a case of Amex trying to scam you because you’re using a flight credit. It is more likely an Amex inventory availability issue.
On a couple of occasions I have booked an outbound leg via the Qantas website and the inbound leg via the Amex site (or vice versa) as the pricing was better.
Also bear in mind that the credit has to be used in one shot and any leftover value is forfeited if the fare is less than $450 e.g. if you book a $150 MEL-SYD flight and use the voucher you will lose the residual $250.
Is there anything else that you’d like to ask/know?