Halon works well in enclosed spaces, not very well outdoors. It is also corrosive so it is not perfect either. It would not have worked well in the 8 or 10 times I have used an extingusher on cars. The dry chem worked on all but the tire on fire, but they did keep the fire supressed long enough for the FD to arrive. It would have been plenty of time to get everyone out even in an accident where you had to cut belts or remove a window (the car was in a parking lot and no one was inside). Although CO2 is probably best for vehicle fires (unless you have foam capability) dry chemical works OK. For engine fires a 10B
:C is usually enough (but I carry more than one). If the car is involved, particularly the fuel tank, the best you can hope for is to supress a pathway to get people out.

For carry I have a 10B:C mounted to the floor in front of the drivers seat mount (under the front of the seat) and a 20B:C mounted on the trunk wall.

Respectfully,

Jerry