They are actually a set of 'single use' or 'event day' cleats. They are designed to be clipped in once and have to be destructively removed and discarded for safety reasons immediately after.
They are the same weight as regular cleats, and you can't tell the difference until you try to clip out for the first time. It is used as more of a motivational tool among racers, to put them in a 'do or die' mindset.
They were removed from the market after the gruesome death of the entire Lotto-Fuji squad in 1996.