We had a pleasant stay at Elvin's place. We arrived late at night and it was no problem for the check in. Also, communication with Elvin was easy and fast.
The flat is in a great location to move around Istanbul. You can get to Hagia Sophia walking in 15-20 minutes and at the very top of the street you enter the Grand Bazaar. There are many restaurants at the bottom of the street nearby, which seems to be a nice residential and quiet area, with good food prices.
As other comments noted, the flat is only 400 m away from the tram station, but the flat is at the bottom of a very steep street; something to consider if you travel with old people. However you can easily find taxis at the bottom of the street.