_pretty harmless material_
Ball bearings (like what is on your crankshaft) are what is called "zero clearance bearings", meaning: there is a very small amount of room between the balls, and the races, The introduction of ANY foreign material (that the bearing can't smash out of the way) into the bearing causes immediate failure. Reeds are not going to break off at low RPM, maybe your engine will stop before that bearing spins on the crank, or in the case, or maybe it won't.
Reed valves should be replaced @ rebuild time.