I had a great stay at Christian's. He was very lovely and accommodating.
The room was very cosy, and the proximity to the U5 allows you to get to the centre of Berlin very fast. As a bonus, the bathroom also gave me the best view of the sunset over Berlin I've ever had while brushing my teeth! Overall, this booking was a lot more comfortable and quiet than other rooms I've rented in Berlin in areas like Kreuzberg.
I would 100% come back.