The stay was very nice. The location with regard to the trains around and the night-life (hipster/grungy) was great. Furthermore, the hosts were VERY helpful and very nice people. They would hold themselves out to be reached whenever needed and were quick to accommodate an unexpected guest of ours too. Furthermore, the apartment was extremely spacious, secure and clean.
The one downside to the stay was the proximity to Kotbusser Tor, which is a sketchy train station. However, the hosts did make it clear to us upon arrival that we had the option to take another train, which was only 2 minutes walking from the apartment. This other train station was very nice and just as convenient as Kotbusser Tor. And the truth is, with a minimum amount of street-smart and vigilance, the proximity to Kotbusser Tor should not ever be an issue.
Other than that, the stay was quite good and I would recommend this place to anyone looking to stay in Berlin and have a great time going out.