Those would scare the dickens out of me. I'm sure they have been tested and all, but I imagine about 13 different ways that could go wrong. I have seen similar things on old Ford tractor ads and thought it seemed cool. It takes on a whole new dimension when you put that on a vehicle that goes faster than 10 miles an hour.
There are certain feelings you can't explain other than to say it causes your rear end to pucker. This would be one of those times.