I stayed at Jürgen's with my partner and daughter for 10 days. The purpose of the trip was to spend time with my family who live relatively close by.
The flat is very spacious, comfortable and clean. It is very easy to feel at home and relax. The kitchen is well equipped and both kitchen and bathroom are modern. The bed is very comfortable, and the blinds keep out all the sunlight so it is easy to have a lie in.
Jürgen and his wife are very friendly. On top of the normal hosting, they organised a child seat for us and helped us out with some butter.
The house is in a very quiet suburban area with the family friendly FEZ park nearby. Going into town takes about one hour so probably not recommended for first time Berlin visitors. If you want to focus on Köpenick and the south east then I would highly recommend Jürgen's place.