I would say definitely worth doing on a sunny day. It was pouring when I took the tour. Still got some great photos. The boat operator offers everyone fresh orange juice & insists that you take one - then charges you for it. Met some very nice tourist on the trip.
I was the only person on the tour. Tour guide was an excellent guide. Definitely a tour to do when you first arrive in Istanbul. The lunch at the Topkapi Palace was great too. Incredible view of the Bosphorus from the restaurant terrace. Best tour of my trip. Thanks!