Martin's place is in a really good location, it's in the middle of a couple of U-Bahn/S-Bahn stops, but we also used the bus quite a lot too. It's a few minutes walk to trendy Kreuzberg, with lots of highly recommended restaurants, including vegan restaurants.
Martin was really friendly, greeting us himself at check-in and offering good advice about the local area.
The apartment itself was really suitable for us, two couples and two infants. It is in the basement, with about 6 or 7 steps down, much preferable to going up, and with a nice wide doorway for pushchairs and suitcases.
It was great to have a kitchen, it saved us a lot. The beds were really comfy and the apartment was warm.
Would recommend for sure!