We sailed on a Dream MED cruise last year. We did the Hidden Santorini tour so unfortunately I can't offer any specific info on the Selfie tour. What I can say is (1) Santorini is really awesome, and (2) make sure that your tour takes you back to the main ferry/boat launch dock where you get off the tender. Many tours end in Fira (high up the cliff), or they give the option to stay and not ride the bus back down to the ferry dock. A lot of people stayed to eat and shop and thought they could take the finicular down to the secondary boat launch. The line was 90-plus minutes long, so many had to trek down the steep path to make it back on time.