We really enjoyed our stay at Ellen and Malte's place! It is very clean and tidy. They were quick communicators and very accommodating. The local transportation is very close (4 min walk) to get to/from Tegel Airport and all the Berlin sights. There are plenty of local neighborhood restaurants to eat and drink. It's also near the Berliner Mauer, which you must check out (best spot for Berlin Wall history). The apartment would be tight for 4 adults, but definitely doable. There were 3 of us, and we were very comfortable, although we were out most of the day. We would definitely stay here again.