I stayed at Francesco's and Elisa's appartment recently with my mom and should say, it was a fantastic stay for us! The appartment is extremely-cleaned, well-furnitured and equipped with everything you might need. Francesco and his wife were really helpful and that wonderful teas selection they left us, was a real treat when we got sick.
The appartment is close to everything. There are at least 2 Underground stops within 5-mins walk which makes connection with the rest of the city really easy and quick. And due to proximity to the Tegel airport, a 10-mins taxi drive from there does not exceed 16 euros.
I would definitely reccoment this appartment for everybody who wants to enjoy his stay in Berlin and cares about his comfort.