I work for one of America's 25 largest cities. Within the past year, a few patrol officers have been issued CATs. I am not aware of any of them being used. However, we have had numerous (5-10) uses of privately purchased and improvised uses of tourniquets going back to at least 2009.This includes an amputation of a leg when an electrical tower fell on a car and officers being shot.
We had a sergeant shot in the leg during a raid, and a fire fighter applied a CAT to him, then pulled him to cover, which was exhausting. However, either he didn't tighten it, or the windlass came out of the little u shaped part because he didn't secure it with the white Velcro strap. The sergeant was bleeding pretty heavily from the leg wound when I got there, so I asked for a second TQ. While they were digging one out, I double checked the original TQ, found it wasn't tight, and cranked down on it, stopping the bleeding. The sergeant later told me that the TQ hurt worse than the original wound. I have heard that's common.