These are definately worth having. My friend used one on an engine fire in his rally car.I have two of these, one mounted at head level just inside the hab door, and a second at floor level in the same location. Both 50 second usage time. They are expensive, but so is my van. In all probability if fire took hold, no extinguisher will save the van, but one takes whatever precautions one can.
Fire Safety Stick fire extinguisher
firesafetystick.com