Overall we had a pleasant stay. We especially liked that the the apartment is in the basement from one side and ground floor on the other side (due to Istanbul being a hilly city). So the advantage was that it was not hot at all even outside temperature was quite high. So if you travel in summer then it will be a perk. Vedat always replied promptly to our messages.
Take into account though that the apartment is located in a side street and not at all in the heart of Beyoglu which means that you always have to walk at least 5-10 minutes to a street with multiple restaurants.