I’d highly recommend this place.
The location is perfect: easy to walk anywhere or use public transport when needed, it is close to Şişhane metro station, ferry station and tram stop.
The apartment is lovely and well equipped. Special thanks for candles to create the atmosphere for rainy evenings. Also there is very nice view from every window. Mind that the flat is on 5th floor and the stairs are pretty steep. Also there is a small issue with the shower: it is not possible to regulate the water temperature, we always had kind of contrast shower, from very hot most of the time to bit normal. But it is not a big problem.
Zeynep is very friendly and quick to answer all my questions. Once there was a problem with the water heater — she resolved it within an hour! I cannot even imagine how it is possible in such busy city as Istanbul :)