Stayed here for about a month. It's a perfect place located in a touristic neighborhood, but on a lovely and quiet street (we haven't heard any loud noise - not partying people, not local calls for prayers). This flat has a heating system and AC, so in hot and cold days you'll have a comfort temperature at home. Good quality WiFi Internet (two parallel video conferences had no lags).
There are a couple of shops around (beware of those which don't have price tags) and good restaurants (I totally recommend Arada cafe on the corner). We never used a public transport (except ferry) because everything was pretty close to apartment (Dolmabahce Palace in 15 minutes walk, Galata Tower in 5 minutes walk, Blue Mosque and
Hagia Sophia in 30 minutes walk). However be prepared to a very hilly area (hills are everywhere in Istanbul).
Sabahattin replies very quickly and gently. Once we had a minor issue with water heater - it was resolved in less than 30 minutes.
To sum up: next time in Istanbul I will try my best to rent the same place. 10/10.