Air Jack/Exhaust jacks
 

I was just looking around at random stuff and was watching some videos of exhaust jacks they seem kinda cool, but has anyone actually used one? they kinda seem unsafe and a little scary to use, I could only image what would happen to a person if they were under their rig and the bag popped or got a rip in it
http://4x4fever.com/images/exhaustjack.jpg

i think with those bags you're supposed to set it on jackstands once you get it up.