I originally booked for two nights here, but ended up staying 8 more nights.
The hostel is in a very quiet and chilled-out neighborhood which I found great. It's on Asian side so you have to hop on the ferry to get to the more touristic places on European side, and if you wanna have late night parties in Taksim area, you'll need to hire a cab(40-60 liras) or get on a dolmus(5-6 liras I think) to get back to the hostel. This might be frustrating to some people, but I had no problem with it. If you're a group of people, I think it should be fine getting around.
As for rooms, I stayed two nights in fully ensuited double room with AC, one night in a dorm, four nights in a single room, and three nights in a double room.
Ensuited double room was amazing. Mattress seemed a bit old and sunken but very clean and fresh with beautiful sunlight from a high window.
I just slept one night in a dorm room without spending much time in the room but it was okay, clean room with high window as well.
The single room I stayed in was on the other building which is across the street from the building with reception. It was also clean and shared shower was more spacious. Only thing is that it was a bit warmer than the rooms in the other building(I'm not sure if it was only the room I stayed in). I assume the air flowing there was less and the room was a bit compact so it heats up.
The double room was in the reception building and it was fresh even without AC.
The hostel only has a spiral staircase so if you have a heavy luggage and get a room on upper floors, you might have to be ready to hassle a bit.
The breakfast is simple Turkish style. Bread, cheese, tomatoes, cucumbers, ham, cornflakes, and some fruits. It was good enough for me.
Overall, I had a very pleasant stay at Hush. It was a pretty long stay and I never had any complaints that I had to talk to the staffs. Staffs were always very helpful as well. I'd definitely stay here if I visit Istanbul again.