San Francisco ER doc here. See a lot of older dudes who weren't skateboarders to begin with breaking bones on these and more traditional longboards. I am a former skateboarder, and certainly don't think that longboarding is inherently unsafe but when you add in a motor and make it easy for someone to learn to use a skateboard without putting in the time (and inevitable falls) at lower velocities, and compound that with a hilly city with a lot of unpredictable traffic, badness occurs. Just be careful, wear a helmet, skate defensively and please don't play in the streets until you're ready.