[jmaxwell]

One of the contributors on the 914 board had an experience with the types of jack stands shown above, where the jack stand released and collapsed while he was under the car, flattening his nose and other parts of his face. He didn't remember hitting the release or bumping the jack in any way, so how it released is a mystery. It was under the trailing arm, and luckily did not tip over, but just went down to the lowest position. The conclusion there was that while the quick release functionality is very handy, you should always use stands that have a safety pin in it as well.