We stayed at Istanberry for a recent weekend in Istanbul, at the end of 10 days traveling around Turkey. The apartment was immaculately clean and looked just like the photos. The neighborhood is definitely "local" (not touristy). You can easily walk to the Istiklal Cd street which seems to buzz all day and night. The market across the street from the apartment is open 24 hours and is convenient for buying bottled water, etc.
We found the host to be very kind, responsive, and helpful when needed. For example, a hair dryer was missing from the apartment when we arrived and he immediately replaced it; he helped us with wifi issues and also organized a taxi to pick us up for an early flight on our departure.
The downside for us: for a weekend stay, we found the Istanberry location did not work well for us. We weren't familiar with the city and despite the distance estimates provided by the host, we mistakenly underestimated the time it would take us to walk to/from the main public transportation hubs. The location might be perfectly fine for someone living in Istanbul for a week or longer--again, you're well-connected to a popular shopping and nightlife area to explore and just "be." But, since we were only there for the weekend, we lost a lot of our brief time commuting.
Further, it was raining hard our entire weekend, so in a couple instances we would have preferred to take a taxi to stay dry. Our experience was that several taxi drivers either did not know the location or refused to take us to a nearby drop off point since that particular area was difficult for cars to get to. We live in a city ourselves and usually prefer to take public transportation or walk (vs take a taxi), whether at home or when traveling...but since it was raining that weekend in Istanbul and the walk to the tram/funicular stations was long enough to get very wet, this was inconvenient. In hindsight, for a weekend in Istanbul, we would have preferred closer proximity to a public transportation station with easy airport access, so as to have more time to enjoy the city itself. We'd also stay longer than just a weekend! :)