The apartment is really nice. The sea view is really inspiring especially at sunset. Everything is super clean and comfy. The only thing missing is the washing machine, but they provide laundry service. All other amenities are very new and complete.
We stayed for 3 days and we didn't need transportation for visiting most of the old city landmarks like Hagia Sofia, Grand Bazaar, Islamic art museum. Only few minutes of walking which we enjoyed in the nice weather. Safe box in the apartment was an important part of the amenities, which most other apartments doesn't have. I checked few others who have written as the safe available in the amenities, however when I asked them about it they told me they don't have it. Seems they thought that the safe means that the apartment is safe :). If this is important for you ask the owner before you book. Ercan's apartments all have safe boxes (as he told me). It was important for me to put my money and tablets/laptops with my own password. This was something that provides me piece of mind during my trip and allowed me to not call all my money in the streets.
Ercan and his colleagues were very helpful and responsive. They even let me check-in early at 8 am since my flight arrived around 6am. He was happy to help me with that as long as nobody was staying in the day before, which was that in our case. He even offered me taxi transportation from the airport to his apartment for an extra fee, which was nice.
I would recommend this apartment for anyone who wants to stay near the old city of Istanbul.