About the flat: it was very clean, the kitchen was well equipped with most of what you would usually need, including microwave and a big fridge. The place was quiet and the location is very good with an S-Bahn station and supermarket 10 minutes away by foot.
About the owners: Annette and Ulf are super friendly people and they always reacted fast and helped me with any issue I had.
I stayed there for a month and I can totally recommend this place.