Sorry that it wasn't clear, but I have the discounted AARP gift card already. There's an option to pre-purchase OBC on the website before the cruise starts (which you can pay via GC), so I wasn't sure if there were any advantages to pre-purchasing it vs. just adding it on when you're on the ship.
When buying OBC with a gift card, is it generally recommended to add it on at Guest Services when you're on the ship, or is it better to pre-purchase it through Holland's website before the cruise? Either way, this would be considered refundable OBC, correct?