Re: semi metallic clutch pucks
I looked in there to grease the gears when I built the bike. The rubber pads appeared to be adhered to the clutch pad rotor somehow. It would seem foolish to not have them attached to that, as when releasing the clutch, a pad could come loose and lodge somewhere it shouldn't be.
I am sure they will make much more debris if used as a conventional clutch, to slip it when taking off from a stop, or riding a lot/idling with the clutch disengaged. I hope to make mine last longer by pedaling to take off and engaging only at a speed that it will slip the least and engage the quickest.
Also, the rubber dust/shavings should pose less risk to damaging the gears or bearings when contaminating the grease compared to the harder brake shoe pieces suggested in post #1.