I really enjoyed my 4 days stay at Hostel KW Sinsa. The instructions they email you prior to arrival was super easy to follow and the hostel is a short walkable distance from the nearest subway station. Check-in, while a tad on the informal side (there is no reception/lobby, just a check-in room in the basement), was super quick and I was shown to my room straightaway.
The room was, in my opinion, fantastic for the price I was paying. It was more like a furnished studio apartment than a hostel room. There was basic kitchen appliances, including full-sized fridge & stove-top if you are keen to cook, plenty of cupboard space, TV, even a washing machine. Everything was tidy, neat and clean. The free wifi was definitely a bonus. I was pleasantly surprised.
Some minor things to be aware of: minimal hangers so bring your own if that's important, no cleaning services during your stay, which didn't bothered me at all as I liked my privacy and knowing that I can just place my things around the place as I see fit. And for the rate you pay, it's a great deal.