a few tips for use:
make sure that your exhaust pipe is leak free and sound!
use the engine on tickover, no need to rev!
make sure that the pipe from the exhaust to the bag is in a big wide arc, with no kinks or twists in it.
put a touch of air in the bag before attempting the actual lift (if you can). not so much that you trap and cant move the bag, but enough that it will be touching the ground and the underside of your car with enough pressure to be able to move it about, adjust the folds or reposition it slightly.
put only 2/3rd to 3/4s of the top of the bag under the sill and angle the bag very slightly, inflating very slowly at first so that the bag will create a similar but smaller angle when inflated to how the car will list over...then hit it with full pressure in one hit for the lift. while matey stamps on the brakes.
make sure that the input hole where the pipe attaches, is pulled out sideways and is not trapped in any of the folds. once pressurised, if the pipe is trapped in a fold you wont be able to release the pressure without a full lift as you cant twist the pipe off, not good if you've got it positioned all wrong..!
use a carpet tile or your rubber footwell mats to protect the bag at the top, it has spikes on the bottom so dont use anything at the bottom unless you fear it's gonna get punctured.
the sides of the bag are more prone to tearing, keep a lookout for the hockey stick bolts, steps or mudflap bolts that may damage the bag, and if it touches them in danger of a rip, whip out the pipe and deflate rapidly for less chance of a tear.
the repair kit is a waste of time, dont tear the bag.
to bring it down, twist and release the air very slowly at first to control the fall, when the wheels are just an inch off the ground whip out the pipe and get out of the way, otherwise you get a face full of exhaust gas!
Hope this helps, and hope you dont have to use it on your journey, but when you do you'll be dam glad you bought it...!!