This flat is really good : well placed in the city, very peasible and well equiped except the hob which is not the best. It was clean and comfy with a nice garden and a little terrasse to chill under the sun.
The only trouble we had is the communication with Ekhart who was quite quiet, we had to wait an hour and a half in front of the door without any news when we arrived.
Viktoria Park, which is one step away from the flat, is incredible with a safe and cool vibe. There are also many good bars and restaurants next to the flat.
We rented bikes during our 3 days trip, it's a great way to visit Berlin if you want to cover it all. 360 Rad is a great store to rent those (25-30 minutes to the flat walking).