Uber in Berlin is kind of a joke. With UberX you never seem to be able to get a car, and for calling a taxi Uber is simply nowhere near the best app out there. There's at least two German apps with better functionality for that purpose.

With regard to safety, I think Berlin is still OK but it does seem to get worse every time I go. In 5-10 years I guarantee that question will be a lot more difficult to answer.