On the luxury cruise lines you will get a $300 onboard credit but only Silversea gives your the bottle of Dom Perignon. Others will give a bottle of wine, a bridge tour or other amenities instead in addition to the OBC. More mass market lines will usually give a cabin upgrade instead of the $300 OBC. If you cruise more than once a year the card pays for itself. Even with only one a year you have paid for two thirds of the fee.