The communication and checkin process was really easy, with transportation from the airport and the host waiting for us in the apartment.
Gulnur explained everything about the property and the area, they have a folder with very useful local tips. She replied quickly to our messages whenever we had questions.
The apartment is spacious and bright in a quiet street, fully equipped with anything you may need, including dishwasher, washing machine, dryer, cooking utensils.
It is on the second floor by stairs and up in a hill, something to consider if you have mobility problems. However, there's a not-so-hilly way to reach the main attractions in Sultanahmet, which are 10-20 minutes walking (Haguia Sophia, Blue Mosque, Topkapi palace, etc). The tram stops 5 minutes away (a bit of a climb on a hill as well).
You can see the sea from the balcony, which is a great sight in the evenings. However, right next to the building there's a semi-demolished construction with some trash that make the view a bit less appealing.
Internet was poor, but I found this to be the case almost anywhere in the old part of Istanbul.
In summary, great host and a nice apartment close to the main sights, yet not in a noisy place full of tourist.