This apartment is highly recommended. The location is amazing (right next to alexanderplatz) with tons of restaurants close by. When we first came to the apt someone was waiting for us there, greeting us and making sure all is ok.
On our last day we asked Nadia if we could check out at a later hour (as our flight was late at night) and she replied within 10 min saying it won't be a problem at all.
The apartment is awesome. The living room is big and comfortable, the bedrooms are cozy and the whole vibe is just great.
I highly recommend this place to anyone visiting Berlin.