Yes, I have only redeemed once, but twice....
I went into Hungry Jacks and they had no idea. The young girl was completely perplexed and so she called her manager and I showed her (manager) the email you get when you type the code in. She went to the register, saw the NBL code and hit it. Got me a free burger.
BUT... when you hit the link on the email it takes you to the NBL app and there is a green button to press to redeem.
Later on that day I went back to Jacks to let them know about the app, and tried to tell the (now different) manager that there is an app to press. She pressed the green button and gave me a second cheeseburger....