Actually, I think taking the regular ferry would have been more convenient. The pick-up and drop-off service takes a lot of time, and you can only spend two and a half hours on Prince's Island, not enough time to hike up to the top. Afterwards, I spent about an hour at a leather clothing store (round-trip transportation + sightseeing + shopping). If you don't go to the store, you have to go back to the hotel yourself (I chose to go to the store because I didn't want the hassle, but it turned out that taking the bus back would have saved more time). Overall, however, compared to other tours in Istanbul, the price-performance ratio is acceptable. If you're willing to spend a whole day exploring the islands, you can give it a try.