Hi JN,
I also have one and find it useful, to get the car at a good working height---or at least better than it would be with conventional jacks.
To be clear: the way the quickjack lifts the car is exactly the same as a conventional lift would: there are four support points, and they are the same points as would be used with a lift.
I know it sort of looks like the car is supported along the entire length of the rocker, but due to the rubber blocks that Pawel mentions, there are only two support points on each side, one at the front and one at the back.
Meyer