I didn't see Mustafa but he answered all of my questions and was welcoming. The studio looked nice, just as it's shown on the pictures - simple and modern design. I also liked the shower, there would be enough space for two ;) There is everything you need in the apartment: tea, coffee, kettle, microwave, kitchenette, shampoo, towels, AC, etc.
You need a code to open door. Furthermore there are surveillance cameras in the building. Mustafa's assistant and sometimes his father are sitting in the office on the ground floor to ensure safety. So, you don't have to worry about that.
The area around the house doesn't look nice but it's well situated near Taksim Square and Metro Station (4-5min walk). There are some mini markets and kebab shops on the same street.
Unfortunately, the Wifi conmection was very slow at daytime, however it became fast at nighttime - I think too many guests in the house sharing the same Wifi at daytime.