The apartment is in a good location, in a clean and safe area of Berlin, close to good restaurants, 2 lines and 1 tram line. The room (American kitchen) is big enough for 3-4 people.
The flat is on the ground floor, directly opens from the street, but there was no problem with it. The self check-out works fine.
Hans and Ute have provided instant support whenever needed. Thanks for everything.