Most grocery stores have "Mart Carts" or similar electric (sit down) scooters for customers that have disabilities. These are more of a commercial grade device. They're meant to be continually used, recharged constantly, and have at least a few safety features such as a beeper that sounds when backing up, and the speed limited to a couple of MPH. They are also a bit more rugged and probably have some degree of weather resistance.
If cities are going to rent scooters, there needs to be a similar type of unit for rent. Perhaps one that can detect when being ridden on a sidewalk and slow to a walking pace, one with more safety features, and perhaps with lighting and/or reflective portions to make them visible to motorists.
But I have to say to the people that were injured by tripping over these--WTF? And are we also going to sue skateboard, rollerblade, and bicycle manufacturers because people are idiots and meet mishap without bothering to wear any safety gear?