We had a nice stay with Project A. The room was bright and clean, bathroom also very clean.
First time being in a zero-waste household and it was a good experience.
Contact with the host is also very good and clear.
We had a late check-in and this was no problem with the keybox (extra 5€ charge)
Subway is also very close (walking distance) and you are in the center of Berlin in no time!
Small minus is the old hallway - you have to lower your voice for the neighbours and once inside the building it's shared with another guestroom (which you share the bathroom with) you also have to watch your voice with respect for eachother. But this was not a big problem for us.