Irrespective of the views of BBC Berlin, I lived there for many years, walked, cycled, ran and drove and the most unsafe I felt was whilst driving. Riding a bike there was, and is a joy for a city. The OP quotes about 10% wear helmets, I would say less, and why would you? Cycling in Germany as a whole is very probably the most relaxed mode of transport, all those that wear a helmet over here could do a lot worse than taking a ride without a helmet over there just to see what it feels like.