We stayed in the appartment in three, but there would easily have been space for two or three other people as the appartment is really spacious. The appartment is exactly how it looks on the pictures (newly renovated, well designed, homey, very clean). Although we arrived later than foreseen (the tranfer from the airport to the appartment was perfectly organized by Izel on our request) Izel took the time to explain us everything regarding the appartment and the best ways to explore Istanbul. He gave us a lot of really good recommendations of things to do and places to go, even taking us for a walk around the neighbourhood. The area where the apartment is located is a perfect starting point for sightseeing (you can either walk or easily use public transport from there). The house is in a rather quiet street but less than a minute walk to many nice shops, restaurants ecc.
We would definitely recommend CasaLoBueno and surely will stay there again if we come back to Istanbul!