We stayed at Kubilay's home for 3 nights with my boyfriend.
Kubilay has been a great host, very kind and helpful, he made us tea, breakfast and we even had dinner with (so we could discover some delicious specialities).
It's a very nice person and he makes his best to make you enjoy your stay.
The room is very clean and tidy, the bathroom too, nothing to complain about.
The flat is not in the center of the city, so you'll have to take the bus for 15/20 minuts to get to Sultanahmet, but it's worth it because Kubilay's neighborhood is nice, not turistic it's more like a typical turkish area, so you can taste real turkish food (and it's really, really cheap, and delicious).

We really enjoyed our stay in Istanbul, don't hesitate and book this room!