We had a great time at Demir's place. It is located in a fantastic neighborhood (Moda or Kadikoy). It is full of energy, with bars, restaurants, and live music. However, you won't hear any noise in the bedrooms so sleeping would be fine. There was sufficient stuff in the kitchen, so we were able to cook from time to time. Demir was very responsive and helped us whenever we needed him. The only issue that we had was a bit of smell in one of the bathrooms, but it was manageable with an air freshener.
In our next stop in Istanbul, we would definitely stay in this place again :)