Went on the Star Princess in June to Alaska. The adult soda card was $17.50. Didn't have to pay an additional 15% tip to the $17.50. Having the card was wonderful. Sometimes, you just don't want tea to drink with your meals, if you are like me. I would get a coke and my husband would turn around and get him a coke, also. No questions asked.
We had the drink card on the Regal Princess and wouldn't do it again. We only had the choice of coke or diet coke. My wife is a diabetic and has to have diet drinks. They had diet sprite in the can but canned drinks aren't included in the soda card. Sodas for the soda card are obtained from the bar and varied from flat to watered down. In addition, since there was no gratuity added to the card purchase, it was difficult in some situations to get a soda, like at shows. They'd take your order but never return.
Our grandkids also had the soda cards and drank too many sodas because of it. On a previous cruise they had a lot of milk with their meals. On this last one, all they drank were cokes. It did pay for them because of all the sodas they drank but its not something we'd like them to do on a regular basis - ie - drink that much.
We purchased the soda stickers for all 4 of us (2 adults, 2 kids) and found it to be very convenient and certainly worth it. However, we are big pop-drinkers. Last time I cruised, I carried my soda onboard with me and bought more along the way. That was a hassle, especially carrying it when you are lugging all of that heavy luggage. We ordered soda in the buffet, lounges, poolside... etc and never once had them not return with it. In the buffet it took a few minutes because these attendants are not really waiters, and they had to walk to a bar and order the soda for us. So I had no complaints at all.
They had a strange arrangement on the Regal Princess if one wanted to put their tips on their cabin account. One went to any bar and obtained a voucher which was just the same thing as one gets when they buy a drink. You had to fill out the tipee's name and position. You then gave that receipt to the person being tipped in those envelopes instead of cash. A little hokey but it was better than taking cash with. (G)