Great location, but.....
The locations is really good, because many of the Berlin highlights are in walking distance and if not: a public transport station is just in front of it.
There are plenty of restaurants/bars below the apartment and a supermarket is just 2 minutes away as well.
It can be loud in the apartment due to the activities on the below square though. (weekends)
As for the interior of the apartment: all good. The description says that the kitchen is fully equipped, but we missed things like glasses and a kettle for hot water. (but the host informed me that they will get a kettle soon).
When we arrived there was laundry drying in two of the rooms. That gives somewhat a weird impression. We also found eggs and alcohol in the fridge as well as some other groceries in the cupboard. (sugar/coffee, salt, etc)
Clearly left by previous guest, but not everything was useable anymore.
During our stay, we could not get any hot water in the kitchen nor could we get the tv working.
Communication with the host was slow or not existing, but in the end we were offered a small discount for the inconvenience.
As for the retrieval of the key: not ideal: we had to look for it in the dark (under a bridge) and when we found it, it turned out that the key locker/holder was laying on the ground covered in all kind of dirt (and worse).
Due to the location it will be attractive to many visitors, but I would not book it again.