We travelled to Berlin in May this year and stayed at the apartments for 5 nights in a large family room with 3 bedrooms. We were 4 adults and 2 children and the apartment was really big enough for all of us with a huge master bedroom and 2 smaller bedrooms with twin beds (no fuss about the Twin beds, they could be put together).
The apartment is very centrally located at Gendarmenmarkt with underground connections just around the corner, but who needs the underground if all the tourist attractions and shopping areas are a short walk away. The area around the apartment has quite a few bars, restaurants, cafes (although expensive) and even a supermarket a short walk away.
The apartment itself was quite big with 3 bedrooms, 1 bath/toilet, 1 equipped kitchen with all appliances and a large comfortable living room with a balcony. Couldn't ask for more after a long day of touring and shopping. The apartment however is a little dated and could do with some re-refurbishment and a lick of paint, but since we were mostly in and out of the place it didn't matter. We were there to see Berlin - Not buy the apartment!
Overall - Extremely satisfied with the stay, would definitely go back some day & recommend to anyone.