My wife and I have been to Passion Island twice and thoroughly enjoyed it. Passion Island is a fitting name for this exotic little place. With everything included in this excursion (drinks, lunch, use of beach items, etc) it is a good value.
As for tips, a dollar here or there is much cheaper than in the US or Canada for any touristy spot.
Carnival Liberty New Year's Eve 2007
Liberty of the Seas 5/2008+11/2009
Allure 1/16/ 2011
Vision OTS 2-14-2015
Freedom OTS 3/6/16