TL;DR:
Stayed in the apartment for 5 days in early October. The place was great for just the two of us to come for a few days and catch our breath, but for the longer term, it'd be better to find something else.
What we liked:
1. Location. We already stayed at the house across the street last year, and now responsibly confirm that the location is very good. The neighborhood is tourist-oriented, and almost everyone speaks English, so there are no problems with communication. There are several grocery and fruit stalls within a two-minute walk (but it takes a longer walk to the chain supermarkets). The İstiklal Caddesi is about a 7-10 minute walk. Galata Tower is about the same distance. To Hagia Sophia and the Old City to walk for about 40 minutes. A potentially important point: the apartment is on a hill. In some places, there is a steep ascent to it.
2. Communication with the host. The reception is open 24/7. With any questions or problems you can write to messenger, and the answer will be within a few minutes. At one point we found that the door to the terrace was broken, we wrote to the host, and the door was fixed within a couple of hours, despite the rather late evening. Thank you!
3. Space. The apartment really has a lot of space, you can safely stay with two people. The rooms are not separated by a door, but it's still not a studio in the classic sense: we both actively worked, often calling at the same time, and still did not interfere with each other.
What moments confused us a bit:
1. A slight smell of dampness. It lingered throughout our entire stay. Presumably, it could be due to the fact that the apartment is on the first floor, but that's not certain. It does not interfere with life, but when you enter the apartment from the street, it can be felt quite sharply.
2. Far from new plumbing in the bathroom. The shower was hanging by thread: when trying to fix it in an upright position immediately fell, and the bottom tap frighteningly protruded from the wall, fixed by something that visually resembles installation foam (sorry, I'm not a sharer in repair and do not know exactly what it was :)).
3. "Paper" walls. What was going on next door, we heard at times better than what was going on in the next room. Particularly stressful hearing in the bedroom: you get the feeling that you can literally participate in the dialogue between guys from the apartment behind the wall.
To sum up:
Not bad and a fairly spacious apartment for a short stay for 1-2 people, in a great location. The money is great, especially for a short stay. Thanks to the hosts!