The buckets are a good deal, and for a more vital reason than just being a couple bucks cheaper than if you bought four separate beers. They are the coldest beer you will find on the ship! The bartenders will replenish your ice if you ask. I've brought them back to the cabin and left them sitting on the deck, come back later and discovered that my attendant had dumped out the water and added fresh ice.
One thing to note is that if you order bottled beer from a bar by the pool they will not allow you to leave the bar with the bottle. In those situations they have to pour the beer into cups and put them in the bucket. Not a good scenario. This disappoints Corona drinkers.