Mert's place is located very close to the Sahil (pier/seaside) in Üsküdar, which means in less than 2 minutes you'll be greeted with one of the most stunning views in Istanbul. The apartment complex is gated with on-site security, so you do feel safe during your stay.
It's also very close (10-15 mins) walk to the ferry port and marmaray train station, and in between there are numerous cafes, restaurants and mosques.
I was grateful for Mert's flexibility with my check-in/check-out times. I had the place to myself for a couple of days while he was away, and his communication on Whatsapp was sufficient enough for me to find my way around his house.
When he did arrive, he was easy going and gave me my private space, but also provided advice about Istanbul when I asked.