Toxicity can be a problem. It is called CS after the names of the two British chemists who invented it in the late 1920's. It is measured by percentage but that means nothing in and of itself. Some peppers are hotter than others as we have all noted at restaurants. The Scovel taste scale runs from about 500,000 to a couple of million.
Sprays work best on people who are surprised by it.
Chemical combinations of above are slightly better. Not many officers carry ultraviolet lights to detect it. It is okay. It shoots darts that may stick in the clothing or body of an assailant with wires attached. Capacitative shock delivered through wires.