Location of the flat is perfect (climb to the 5th floor is a bit tedious the first time but you get used to it really quick ) , close both to metro and all the main attractions (Galata/Sultanahmet) and is on perhaps the hippest party street in Istanbul.
The flat looks exactly like the pictures, clean and cosy. It has all the amenities needed for a long stay.
Derin is a wonderful host and was always a message away when we needed anything ( karniyarik she recommended quickly became a favourite). Her house and Derin are both highly recommended !!