The battle of the analgesics?
Zheng gu shui is a liquid. Tiger balm is a gel. Their basic ingredients are either camphor or mint.
Tiger balm produced in Hong Kong is popular among the Chinese and the Indians, and it is mainly used on the forehead, the temples and behind the ear lobes for headaches in hot weather.
Zheng gu shui is a late comer in the analgesic market. It is a rather pungent liquid of rather dark color. As a liquid, it is used for large muscles and muscle groups. It is not used on the forehead because it is a liquid and it will stain the skin and drip. It would be very, very painful if it ever gets into the eyes.
Tiger balm used to come in a very small metallic case. The case will trigger the security alarm when one passes through a metal detector at the airport. Zheng gu shui comes in plastic bottles.
For headches, mosquito bites and such, Tiger balm is good. For relaxing big muscles and muscle groups, one can use the liquid zheng gu shui. At least, it is cheaper to use zheng gu shui for larger skin surfaces since it is a liquid.