We stood at Güner/Güven's apartment for 3 nights. The place is really clean, so is the big bathroom. The wifi worked without any problems. Also it is truly near to taksim and istiklal. Even if the immediate surroundings of the house can look very bleak and dangerous, we had no problems even at night; and the small minimarket downstairs is open 24/7. Güven let us leave our baggage inside the house on the last day after checkout since we had a coach to take in the evening, he was very nice.
The only possible downside is the floor: We were at 6th floor with no elevator... But it was some good exercise after all :D
We can really recommend this place!