I had a hectic schedule in Berlin, so I only had the opportunity to meet with Frank once upon check in; however, he warmly welcomed me to his creatively decorated flat and was constantly accessible for all inquiries by text.
The accommodations are excellent and well-maintained. It is possible that you may share a bathroom with another guest during your stay, but Frank makes sure to keep it clean and well-stocked with fresh towels. The flat itself is in a very desirable location: the metro is around the corner and there are numerous places to eat (make sure to try Schiller Burger next door). Highly recommended.