We really enjoyed our stay at Karsten's place. The location is a short walk to a Subway stop making it easy to get around (highly recommend city mapper or google maps if unsure what tube to get). To get to the apartment from the airport it's a short bus journey then underground and wasn't too stressful at all.
The apartment itself is quirky and stylish similar to the pictures and we loved how warm and cozy it was when we were coming back. There's a mini supermarket up the road which was really convineient. Restaurants nearby are quite limited but if you walk abit further there are some gems (Co Chu was one of our faves) and like I mentioned before the subway is so close getting around was easy.
Check in and check out was straight forward and easy. Karsten even let us drop our bags off which was super helpful and a great touch as we arrived so early. He also contacted us whilst we were there to let us know of building work which wasn't an issue but it was very nice of him to notify us just incase we weren't happy.
Overall we would recommend this place if looking for somewhere to stay not in the hustle and bustle of the center of Berlin.