I just switched over to the small element fire extinguishers. I didn't want to pay $80 a piece for them but finally broke down. One is next to my driver seat, on the floor and the other on the driver rear pillar by my hatch.
I got tired of the larger ones being in the way. You have to mount them well enough not to become projectiles. In my entire life of going off road, I've only needed a fire extinguisher twice. Neither were my vehicle and one of the fire's, mine didn't have any pressure for some reason. Actually out of the four, only one worked. That's when i started getting them with a gauge on them.
BTW, save someone's vehicle from burning to the ground and see if they replace your fire extinguisher.