We had a great stay in this apartment very close to the public transport. Right from the beginning, the hostess was very friendly, the apartment was very complete; everything you normally miss in a bigger scale hotel/apartment was actually there, ranging from coffeefilters to travelguides. Because it doesn't share the stairway with the hostess, it really felt like "our" apartment right from the start which was very nice.
The name Ruhe im Zentrum really describes the place very well; there's restaurants and terrasses right in front of the building and your only ~15min away from roaming the Alexanderplatz, yet the beautiful court to which the windows open is as peaceful as you'll find in the German capital.