Clean comfortable and safe. There’s an excellent review on this page by someone called Eddie Rich, and I second everything he says. I was familiar with the Ballhaus Club before, and the hostel had just opened when I stayed there. Excellent wifi, very clean everywhere, and friendly helpful staff. I was usually staying with friends on the other side of Berlin but it was more economical to stay at the Ballhaus than travel by taxi. Definitely good value and highly recommended.