My brother is a police lieutenant in a major LE agency in Southern CA. He has used OC on hundreds and hundreds of people.
I ask him this question:
What percentage of people that you sprayed with OC remained combative?
Here is his response:
"
Maybe 5%, but they were at a serious operational disadvantage. And of the 5 percent, there were often other factors like drugs or failure to get a good, direct hit.
And of that same 5 percent, they were generally not aggressing but trying to get away. It (arresting someone) is an entirely different dynamic. As a tool for protection it is highly effective."
Even if used only as a distraction to facilitate your escape, I fail to see a downside. It only takes a second, and it doesn't limit other defensive moves subsequent to deploying the OC.
If you need a gun, you need a gun, But WAY more often, you won't need a gun. What's in your lunchbox?