We have a similar debate/discussion around fire extinguishers in the small boating world. Having seen both boats & vans go up in flames, I think we’re deluding ourselves if we think we can realistically fight a fire in an enclosed space packed with combustible materials/fuels/plastics etc. If our van catches fire, I’m out of there asap & ringing the insurance company. Even if I did manage to put out the fire, would I want the van back that’s been BBQ’d? All that said, we do carry 2 fire extinguishers in the van, one at the side of the bed & one behind the drivers seat. Both are 1kg powder. I can only see them being used in the event of an external fire or a 3rd party fire. If there’s a fire inside the van, it can take its chances.
If you do carry an extinguisher, don’t just stick it in a cupboard/door pocket and forget about it. Think how & when you would use it in anger & make a plan.
All just my opinion & my take on things, I’m not saying I’m right or wrong.