So you can technically buy $250 credit for $150?
No, if you flight cost $250 and you pay $150, if cancelled, you'll get back $150 only.
Dan is talking in a scenario that you previously bought a ticket full price and it's currently at the same price, in that case it's worth to cancel, get the refund in travel bank credit, then rebook with the promo (you'll end up with extra money in the travel bank).
