I've used Uber in a handful of developing countries including India and China. It's very convenient to be able to set your ride destination without having to speak with the driver, and it's nice to confirm that they took the proper route. However, twice in India I got drivers that were on meth or some similar drug. In India (not sure about China) some people will buy a small fleet of cars and rent them out to drivers to drive for Uber. Uber already doesn't pay well and since these drivers are losing a cut to the car owner they have to drive long hours and so they take stimulants. This is no different than some of the 3-wheel taxi drivers who also take stimulants. Even if you give the driver a low rating the car owner will just rent the car out to another driver.