Saban and Mohammed were very good hosts to me and my girlfriend when we visited Istanbul last week. They were very quick to respond to my emails about things to do and how to get around. The apartment was clean and well kept and is really a 15 min walk to Sultanahmet Square and just down the hill from Beyazit tramway at the Grand Bazaar. Despite what some other reviews suggest, the apartment was pretty quiet.
I highly recommend the flat as well Saban!