As all the other reviews have said, the view from Osman's place is one of a kind, you really can't beat it! We were really lucky with the weather and had some beautiful sunsets from both the flat and the rooftop. The flat itself is located in one of the coolest neighbourhoods in Istanbul and was spacious for 2 people and well equipped. Osman was also very helpful and quick to communicate.
Beware though that the flat is up 4 flights of stairs with no lift and the building is located on an uphill so you will pretty much always have a steep upward or downward walk to get anywhere. Also, if you're sensitive to strong scents, there was a very musky odour that was sprayed before we got there to mask the smell of cigarettes and it made me sneeze a lot and took a few days for the flat to get aired out.
Other than that, our stay at Osman's place was really great.