Gulsen's place is all about the location, he is a very accommodating host who helped us out by letting us check in around noon since we were in town early. He was very responsive to our messages and helpful in his communication. The view is fantastic and the city is at your doorstep with all the main attractions nearby or just a short metro trip away.
The only drawback for us was the kitchen, and for many I doubt it would even be an issue. If you are planning on cooking many meals in the apartment you should know that while possible it will take longer. The flat has a couple of pans and one pot with very basic cooking utensils. However, chances are that you are in Istanbul to enjoy the local food not to cook, and if so the location is perfect, close to so many restaurants you need not cook anything. Gulsen was great and it may be that if you reach out to him, he could provide a few more pans and cooking utensils. Either way you are likely to enjoy your stay at his flat.