Frank's place was absolutely fantastic! The thing that sticks out the most for me was the location. It's in the artist district so the area is filled with creativity and unique spots. There are great places to eat very close by also.. I really liked Floors for coffee, Olivio for food, and there's a bar literally a couple doors down that was filled with locals and very unique and lively. It's only a 3-5 minute walk to public transportation that takes you all over the city, and the neighborhood includes some very gorgeous residential buildings. If you prefer walking over public transportation, that's great too. The place is not so far from many main sights in Berlin and we spent 3 of the 4 days walking around the city.
Frank was a peach with communication and providing information when we asked, and his home is one of the can't-miss sights in Berlin I think! He's done so much to make the place interesting and special. We couldn't have been happier with our stay.