Staying at Andreas' apartment was a wonderful experience. The apartment has a very hipster feel with antique items and furniture all around the place along with a modern feel. The place itself is rather old with squeaking floors (we did once receive a complaint from the downstairs neighbor stating that our footsteps could be heard during the entire night) but is nevertheless comforting.
For me there were two main issues of the apartment. The first was that it was too small for a group of four, granted we were aware of the size of the apartment beforehand. In my opinion the apartment would be best suited for two people. The second issue was the cleanliness of the apartment. When we arrived in Berlin Andreas had been away for over three weeks and his friends had taken care of the apartment and its guests. This would have normally not been an issue had the apartment been clean the first day that we arrived. The fridge was full of food which had gone bad and smelled terribly, there was clothing all around the apartment, the main table as well as the chairs were quite dusty and the bathroom did not look very hygienic. Granted the bathroom didn't look all that appealing when it was clean as well (My only complaint about the apartment itself) as the shower head faced the shower curtain directly and could not be oriented to face the ground making taking a shower a very non-pleasant experience. Furthermore the bathroom itself was very old and quite honestly discomforted me during my stay. This had nothing to do with the way Andreas had kept the bathroom but was rather about the age of the building. But nevertheless this issue of cleanliness all across the bathroom created the need for us to personally clean the apartment, which took two days.
The location of the apartment was ideal, the neighborhood was the famous Prenzlauer Berg and was very relaxing. There were plenty of places around to sit down and have a bite or a drink. As for public transportation the tram and night bus stop was right in front of the apartment and the s-bahn and u-bahn were at walking distances. As a group that tends to go out at night very often we had absolutely no difficulty getting around.
Andreas himself was extremely easy to reach even though he was away and helped us with any problem he could resolve.
All in all I would say that I was pleased with my stay in Andreas' apartment but would recommend you to travel there with a maximum of three people as it is quite small.