Celebrity offers a similar plan so I did some math. With the plan above you would need to have about 6 or 7 drinks a day to make it pay for itself. If you throw in some fru fru coffees this will pay off for some folks. Not for me.
Remember time you spend on shore drinking will not be covered as well.
All I ask is a tall ship and a star to steer her by; John Masefield
Carnival: Glory 2004, Destiny 2008, Splendor 2009, Freedom 2011, Valor 2012, Dream 2013
Celebrity: Summit 2011
Princess: Ruby 2010, 2014, Caribbean 2013, Coral 2014, Regal 2014, 2016, Royal 2017
Star Clippers: Royal Clipper 2015