have to say that any fire extinguisher is better than none, i had mine go up on the A3 just passed Guilford, someone in the other lane was pointing and shouting at me, just as i was about to say "yeah f*ck you too" i heard them say "fire"
needless to say, i couldn't give a rats ass if there was no where to pull over or if there was a bmw in the way, on went the anchors and i jumped out, the only damage was the HT leads, dizzy cap and some other minor cables that were easy to replace....the hand held extinguisher that lives on my transmission tunnel did the job just fine