I definitively recommend this place
The apartment is very well located, close to many (many !) restaurants and bars, yet in a quiet street. It is quite central, and many buses bring you in the different neighborhoods of Istanbul easily (historical district, Dolmabahce, etc.).
It is very well decorated (!), has a nice natural light and a partial view on Istanbul. Everything works well : hot water, wifi, etc.
Nicolas and Taner are very kind and helpful, everything went like a breeze
It was the perfect place for me to spend one week, and I would highly recommend this place to anyone willing to explore Istanbul during the day and enjoy Beyoglu at night.