Clutch Fan difference?

The thermostat type is more efficient, since it drives the fan only as needed. But, it is probably less rugged and it isn't easy to tell when a fan clutch is working correctly. For those that need a thinner clutch-fan, several people have used ones from a Jaguar. M-B fans are also thin and the one for my 1985 300D bolts up to my Mopar water pump w/ the same center hole diameter. They are so short, you can barely get a wrench on the mounting bolts.