We had an overall nice stay at the apartment. Communication with Barbaros was good. He found us even though my phone was dead and he helped us for the taxi from the airport. The room was clean and well equipped with all the essentials. No problem with internet, water or electricity. The location is convenient. There are gazillions of restaurants, shops, baklava stores, etc. around. Is it close to the main attractions of Istanbul. However, kumkapi is a very busy district with toooons of people and cars so it will be noisy in the room facing the street, but that’s the price you gotta pay for staying in the city center :) we got used to the noise after one night :p
The place was not perfect, there were some minor issues such as a window not sealing properly, but nothing too bothersome for us. We had a nice week at Barbaros place.