I enjoyed my 6-week stay. The location is excellent, between Şişhane metro and Tophane tram stops. Istiklal Street is easy to reach on foot. There is a terrific view from the kitchen across the Bosporus and the Golden Horn. Tophane Palace can be seen. There is a very good weekly cleaning service.
It is on a steep hill and the flat is on the fourth floor accessed by a steep staircase with no lift, so you need to be in good health if you are going to stay here!
The flat interior is better in some parts than others. The bathroom is great. The kitchen is nice if a little small. The bedroom is too small to walk around the bed so the wardrobe is in the living room. The sofa and one of the chairs have broken springs. Most of the blinds do not open and close smoothly. There are pans for cooking but no cooking utensils and very little cutlery, and the stove is not very powerful -- so do not plan much catering. There are however plenty of good restaurants nearby.
There is a good TV but only for Turkish, Kurdish and Arabic channels. The WiFi is fine in the living room but weak in the bedroom. The Airco (in the hall) works OK. I did not test the heating. There is plenty of hot water and water pressure for the lovely large shower. The lights work but have switches in odd places.
The landlord was helpful, though I did not meet him in person. I would recommend this flat if you can live with the limitations I have noted.