Klaus was a very discreet host. Meanwhile, he was always up for a cup of coffee/tea and some precious tips by a local Berliner. I had read some complaints about a bad mat in some old reviews, however, imo, this is not the case. My back is really sensitive to this and, indeed, I had smooth sleeps. The position of his apartment is great if you dare to use public transportation. It's really a few steps to both the u-bahn and the s-bahn.