Deniz was very welcoming and is a nice guy. The room is more suited to backpackers who really need to save money, however.

It's in an older building and there is no hot water. The water pressure from the showerhead is a bit weak as well. The toilet seat is wobbly and slides around when you sit on it. Bathroom door doesn't close properly.
You should bring your own towel as well. The one I was given was very small.

Upside is that it is 5 minutes from Taksim square. If you can, spend a little more and get a single room in a budget hotel. Istanbul can be a pretty crowded stressful place so you'll be wanting something as comfortable as you can afford.

Deniz is a nice person, but the room may not be what the usual airbnb customer expects.