As a further comment. other designs I have serious reservations about are stand up forklifts with no safety bar to prevent the rider falling out, electric reach trucks and similar with a singe drive wheel and hence single braking wheel with electric motor plugging, and often a single separate mechanical brake to the same wheel (braking limited by the weight on that wheel alone; failure of the drive can mean no braking or drive at all - I have investigated two such incidents over the past 8 years