Constantin's place was great! We had a really nice time in Berlin, and having this place to come back to was perfect. Very clean, easy check-in, and Constantin is very responsive with messages. We arrived earlier than expected, but Constantin was accommodating and we were able to leave our luggage.
The bathroom is tiny, as is the kitchen space, but we were just there to sleep, and breakfast could be grabbed close by before heading out to do the many things we wanted to get up to. The transit connection is also good. I would stay here again.