We had a nice stay at the apartment. First of all, the hosts are super nice and accommodating (they let us check in early, kept our luggage on the last day and let us use a bathroom after checking out).
The apartment is conveniently located in Sultanahmet where you are likely to spend most of your sightseeing time, in a really quiet area close to many restaurants. The tram is about 15 min walk away, the metro is a bit farther. The terrace has a nice view, although it's probably more useful in summer (we were there in October and it was too cold in the morning/evening to really use it). We did get a few cat visitors on the terrace though :) The place was clean. The kitchen area is very basic but usable. As mentioned in other reviews, there is some humidity smell in parts of the apartment.