If you are looking for a little break from the city and are worried about getting to the ferry to get to the Island(they pick you up in a bus), want to learn a bit about the islands, and have lunch set up for you, this is a great option! The guide was very nice and made sure everyone was accounted for and got to where they needed to. The Island itself is very cute, with street food, sit-down restaurants, cute walks, and shopping available.
However, if you are young and want to explore more on your own and know how to operate the public transit systems(ferry picks up from two locations in the city), then you don't need a tour guide.