How about the GPM Titanium spur only $25 and much lighter than the steel spur and much stronger than the plastic spur.
The plastic spur will melt if the slipper slips too much. And yes the slipper is there to protect the tranny so having a steel or Titanium spur will not harm the tranny, just make sure the mesh is set correctly!!
GPM Titanium spur available in 51T, 52T and 53T $25 from
www.RCXshop.com (plust shipping of course!)