We had a lovely stay at Christin's place and totally fell in love with Berlin! The apartment is in a lovely quiet area, with pretty streets and lots of local cafes & restaurants nearby. The apartment in on the 4th floor so there a lot of stairs - totally fine for us but may be a challenge if you were bringing children or carrying lots of heavy luggage! The apartment itself is lovely, with huge spacious rooms and everything you need. Plus a beautiful little balcony to enjoy sun from.
Communication with Christin was fine but there was a bit of confusion about check in as we weren't clear how we were getting in, having just said we'd arrive around 3pm. Luckily, her sister was cleaning the apartment and was there to hand over the keys but if we'd be 10 minutes later, we would have been stuck. I'm sure this was just a bit of miscommunication and of course this didn't impact our experience in any way.
Would recommend staying here for a unique apartment in a relaxed neighbour, not right in the centre of things but if you're looking for a less touristy Berlin experience and are happy to walk to places, then this is a great choice.