The place is amazing, and well worth the stay. We were 3 friends around 22 y/o staying for vacation.
The host's brother, Emrah, welcomed us when we arrived at 12am in the night and was very helpful, showing us the place and even making the extra effort of going outside with us and explaining where we can eat, drink and get a sim card.
The host's contact, Sabine, was extremely helpful and responsive when our flight was cancelled and had a 1 day delay. Sabine was also very responsive about answering any questions we have.
The apartment itself was very clean and nice, with a big double bed and sofa bed (so we had no issues with space), and also a washing machine, kitchen with a fridge and silverware, and about everything we needed.
The area is great aswell. Location is a bit off the main street so it's not too noisy. There's a gas station with a 24/7 store 30 seconds walk away. The nearest U-Bahn (subway) is a stone toss away (about 2-3 minutes walk) and there are also buses to easily get to any other place in the city (about 10 mins to kreuzberg (kottbusser tor), 20-25 mins to friedrichschain and 30 mins to alexanderplatz). There are good restaurants and coffee places nearby, and alot of döners and schwarmas.
Only downside was no shower curtain and no wifi- I told the host about that and hopefully it will be taken care of.
All in all I highly recommend this stay.