Ship does a lot of selling of the on-off trolly. We used the red, double decker busses which were less expensive, let you sit on top with earphones to hear a guided tour and covered much the same route as the trolly without having to change trollies for the three different routes.
Nice bus ride. Impressive scene. Didn't see a lot of the Island's beauty.
Our own jeep with driver who was very informative and customized the tour to take us to see what we wanted. This is the only safe way to do the narrow coastal roads in the time alloted on a port stay.