Communication with Sinem was great. We never saw her in person but she was quick to answer our messages and since there weren't any guests directly before or after us, she even let us check in and out according to our plans for the day which was extremely convenient. The apartment is very homey, there's great amenities - do not, however, forget to take your shampoo, shower gel, etc as there aren't any of those available, at least not when we were there.
The Kadikoy neighborhood is great - lots of places to eat, lots of nice cafes and shops, cool street art. And the apartment is both in a quiet street AND super close to the buzz and to the bus station and the ferry stops.