I have carried one in just about every vehicle I have owned. I have only had one minor carb fire of my own, and didn't have an extinguisher. I managed to throw enough snow on it to put it out. I have , however seen several other car fires of various kinds, and used my extinguisher to help them out. Even saw an off road mowing machine for a utility company go up in flames after it's brakes caught fire and spread to the engine, tires and fuel tank, eventually completely destroying a $200 k machine. I used up my extinguisher, then used a garden hose 300' long to keep water on the fuel tank until the local volunteers could get there. The company that owned the machine brought me a brand new 10# one to replace the one I had used. Come to think of it, lots of unusual things happened on that property over the years... But yes, much better to have it and not need it... The new ones are much smaller and lighter , so there is REALY no reason not to have one.
Les