I am so glad I stayed in Mehmets apartment. The location is great, just 3 minutes away from Aya Sophia, the Palace and the Blue Mosque. You can easily walk to all the places in the historic old town of Istanbul. Even across the bridge to the lively Beyoglu neighbourhood it's only 25 minutes by foot. The next tramstation (Sultanahmet) is 10 minutes away.
The apartment itself is very small, but it has all you need. Also it's very clean. For a single traveller it's perfect, for 2 people it's possible. You won't be in inside the apartment anyway, since the city is amazing.
Mehmet was nice, he arranged an early check in and a late check out and answered all my questions immediately. I will stay there again next time I come to the city.