The problem with these scooters is that people leave them in awkward places, such as where they block the pavement or a wheelchair ramp. Their wheels lock when not in use and they're really heavy too, which means that some people can't move them out of the way.

With bike rental systems the frustration is slightly less common as you often need to put them up against a bicycle rack in order to return them.

Ultimately this is just a societal issue, but unfortunately there's neither the public co-operation nor enforcement of sensible rules about where to park them in many large cities such as Berlin.