I've purchased 5x of the old "Ultimate Gift Cards for Him" EFTPOS version (card number starting with 5021 25) during the current 15% sale, and thought they would work at all stores listed on the website despite only having 6 retailers on the card.
I've called the reps on 1800 862 126 and spoken with a manager, because the website for the EFTPOS cards is actually different to what's listed in the back of that same card. The website I was directed to by the phone rep was old site which is different than the site listed on the card: new site. What's interesting is that on the T&C's on the "old" site, it directs users to go to the new website for a full list of retailers, which of course includes JB-HiFi et al. Because this is misleading/ deceptive, I've asked for them to be swapped to the current Visa ones which have a much wider retailer set.
They said it is possible, but has to be done manually. The manager asked for a picture of the cards and, pending approval by further managers, they will swap them for the current Visa ones which have wider usability. This process takes 3-5 working days.
I will update here when the process is complete and let everyone know the outcome so you can chase the same process if you've been shafted. If the outcome is negative I will file a complaint with ACCC for the deceptive practice used to sell these cards.
UPDATE: I have received word from Blackhawk that they will mail the new visa cards to replace the old EFTPOS cards. They have manually drained the EFTPOS cards and will mail the new cards, hopefully it's not a scam.
UPDATE 2: I have received the gift cards in the mail via registered post. See image for verification: https://imgur.com/a/YpATMCf
Yet another reason to question how much value you really get from these vouchers when you have to spend all this time faffing around