This is an excellent apartment and I would strongly recommend it to anyone looking to stay in Berlin. If anything, I would say that the Airbnb description does not do it justice. The major plus points, for me, are 1) that the apartment is very spacious, 2) the superb Berlin underground network is right outside the apartment, so you can be on the Unter den Linden in ten minutes 3) it is extremely quiet (even though it is next to a main road), because the double glazing is extremely efficient.
The main bedroom is huge and has ample working space, with a desk and several wardrobes. The second bedroom, although smaller than the main one, has a double bed and is comfortable with room for a chest of drawers and a bedside table. The bathroom is also spacious and the water pressure is great so the shower unit over the bath works really well. The open plan lounge/kitchen area is very large with comfortable chairs and has a small kitchen.
The wifi works well and the apartment is also very clean and well stocked with toiletries and cleaning materials.
Finally, the host, Hubert is truly excellent. He responds quickly to one's messages and is unfailingly helpful.
All in all, this is a great place to stay if you're coming to Berlin.