First of all, the place is located in the backstreet, unpleasant at day, scary at night. despite of Galata is 5 minutes by feet, it won't be a nice walk.
Second, the only window is on the well, blank wall 3 meters opposite.
Third, soundproofing. There is none.
Next, the shower is leaking, towels are not in their best.
Good things I noticed are easy check in/check out, and it was warm inside in february.
I don't intend to dissuade anyone, the place fits it's price and the whole airbnb situation in Istanbul , but you should know your options.