OC is oleoresin capsicum or resin of red pepper. 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. May remember after more sleep.
Sprays work best on people who are surprised by it.
Not many cops carry ultraviolet lights to detect it. Available in a variety of lengths. Choose the length you are comfortable with. Effective and non-liability provoking deployment requires specialized training in their use. Other disadvantages are that you have to be strong enough to beat the bad guy into submission with the baton and it is a close quarters weapon.