This is a great location to stay at in Istanbul. One end of Istiklal CD starts 5 minutes away, Galata tower is around the corner. 10-12 TL to Old City via taxi. The Sishane Metro is 5 minutes away which takes you to Taksim Square and the other end of Istiklal. Lots of good food around the apartment itself.
The apartment itself is awesome, we were 3 families. Two couples and one with 3 children (7yr, 3yr and infant). The apartment fit us comfortably. It has 4 bedrooms, one lounge, and 4 bathrooms (though only 2 are full toilets which are in the lounge area - the two toilets with a basin and shower are attached to the rooms).
Evrim was awesome and extremely accessible and helped us out with shuttle/taxi services for the family with kids though taxi is readily available around the apartment area at all times of the day and night (I got a taxi at 6am for my flight back from right infront of the apartment).