Everything was excellent. Absolutely.
1. The apartment is located near Sultanahmet square, 200-300 meters from Blue Mosque and Aya Sofia. There are two tram ("metro") stations within walking distance (Sultanahmet and Cemberlitas) from which you can go almost anywhere in Istanbul.
It was a little bit tricky to find it for the first time but then we had no problem. Hikmet met us nearby and explained how to get to Sultanahmet from the house.
2. The apartment was clean and cosy. Hikmet gave us even bigger apartment than we booked (https://www.airbnb.com/rooms/4443091). There was all the staff needed there: an iron, hairdryer, microwave and fridge. The bedroom, the kitchen, linens - everything was impeccably clean.
3. There is wi-fi in the house.
4. Hikmet gave us an excellent present: we had huge and incredibly delicious breakfast for free!
I can highly recommend this host and his apartments in Istanbul for all people interested in good accommodation for a reasonable price.