I was in Berlin for a weekend with my parents.
The apartment is beautiful - bright and spacious. It is newly renovated and very well equipped (on top of basics, there are wine glasses, Berlin guidebooks, etc.). It is located in a very nice, quiet residential area (there is a very nice bakery just around the corner). The apartment is 5 minutes walk from the tram, and couple of stops from Alexander Platz.
It was a real pleasure to stay there.
Alex is a very good communicator (he responded very quickly) and flexible (we wanted to pick up the keys late in the evening, which he organized very smoothy).
I will definitely stay in this apartment whenever I am back in Berlin.