This Airbnb is pretty unbelievable. It's an incredible value: at ~$33/night, you are in a prime location, right next to Istiklal street (major shopping and restaurants, etc.). The room itself is also really nice, clean, and beautiful. It is just like in the picture! (When does that happen, right?)
The only minor surprise (thought it wasn't since others said it in their posts) was that the bathroom isn't really sealed off from the rest of the room (there is a door, etc., so no one else in the room could see you, but it's not a bath ROOM it's a bathroom STALL--just a really nice, wooden one).
The only other thing I can complain about is the small bed. The mattress is made out of something that feels like cardboard. I tried sleeping on it for a few days, but it was impossible.
The curtains are really great, so the room gets dark at night. You WILL hear the azan (Muslim call to prayer) five times a day (including at 6am). But I'm not sure how many places in Istanbul close to tourist attractions aren't like that--and, frankly, it's part of the experience. :-)
All in all, I recommend. There are definitely nicer places, but at ~$33/night, this is pretty darn good.
PS A tip: if you are going north, stick to Omer Khayyam st. The rest of the alleys that head north are kind of scary/ghetto. But Omer Khayyam st. is very nice. And the fastest way to Istiklal st. is to take Omer Khayyam st. south on foot. You will pass under the busy street that the Airbnb is just off of.