the belt shredding occured due to the sharp edges of the slots digging into the belts and ripping them. as the pulley wore the problem ceased. he then went to the no slot design to elinimate any further issues.
c3 pulleys are getting harder to find, if the pulley is solid and without excessive wear buy it and enjoy it. mine was bought used and i have had zero problems with the pulley except it temds to wear out my rear tires!!