First of all, Ben's flat is a good apartment, the building and the stairs are elegant and flat is on top floor (careful there is no elevator).
The principal room offers a nice place for work or chill and has the benefits of a big window and good city views, kitchen is big and nice, with a 70's style like most of the apartment. Location is also a nice one in a cool neightborhood, Alt-Moabit, and close from restaurant etc.
Appartement is a bit used and wall paints, especially in the corridor, needs a renovation, bathroom is nice but shower is not convenient and should be changed, bedroom is very small and has no tables.
If summer is very hot , I will not recommend you to take this place because it's too warm especially in the bedroom where it was very difficult to sleep. When I asked Ben about it before confirming my reservation, he says that it will not be so warm and that they war a big fan.There is a big fan , this is true, but I've been lucky that only 3 days of my 10 days stays were very warm, because it could have been very uncomfortable otherwise, again apartment is under the roof.
To resume, this is a nice and big flat so I will recommend it to you, but it's needs a few works and is not the best option in warm summer.