We stayed with my boyfriend for two weeks. The apartment is cozy, in an interesting design style, it is evident that it was furnished with love. Located in the city center; Istiklal Cad. 10 minute walk; to the Golden Horn about 20 minutes on foot under the mountain (the mountain is pretty steep). We like this area, this is the third time we have stayed there.
A couple of features that may be important when booking: the apartment is really small, a studio. For two people it's fine, but for a longer stay we'd still prefer a bigger apartment. It was not perfectly clean when we moved in, we had to clean it up a bit. There is a slight smell of clay and damp in the bathroom, but this is standard for the first floor in Istanbul (at least in this area).
Some of the unambiguous pluses: Internet is good, the speed is high, the two of us could simultaneously call for work or watch videos online. Great location. Very nice, friendly host Mustafa, thank you very much for your support and care during our stay.
To sum it up, the apartment is worth the money, especially if you are prepared in advance for some of the little things that I described above.