Mono leaf springs are perfectly safe. Plenty of OEMs use monoleaf springs, including Corvette since '84 and the 2nd gen Chrysler minivans. I have yet to see one with a failed spring, exept for 1 Dodge Caravan, but it wasn't a breakage failure, but rather the spring eye was stretched out due to a carless tow truck driver thinking the rear spring was agood place to hook up to to pull the van out of a ditch.
I have, however, seen plenty of failed multi leaf springs, with the vehicle ridig on the jounce bumpers.
