As a retired SCCA corner worker I've had the opportunity to put out a couple of car fires and attended fire school for certification I can see it will put out a fire. I haven't looked to see if the smoking stick has a ABCD rating. The small powder extinguishers strapped to roll bars is 5 or 10 BC fire extinguisher. B is burning liquids and C means it safe to use on electrical fires. The number of the B rating means it has the capacity to put out a specified number of SQFT of burning liquid. In the video showing the application of the stick, the user was very close to the fire to put it out. With a powder extinguisher you can be effective at a greater and safer distance.
If it was the only thing you have and needed to put out a fire, use it. Me, I'm use to using power and know what to expect.
A is for wood and paper fires
B is for burning liquid fires
C is energized electrical fires
D is burning metals