I'm thinking of investing in a set of Kreitler 4.5" rollers to replace the cheap noisy and rough pvc drum rollers I'm now using, and have the choice of full aluminum alloy drums or aluminum drums with polycarbonate end caps for $110 less. The question I have is if there is any functional difference that would justify the higher cost of the full alloy drums ? Are they smoother, quieter, more durable ? The Kreitler website doesn't seem to indicate that there is any difference other than to suggest that alloy end caps are more durable and provide more inertia, and I could care less about aesthetics. I use them for spin training and will not be using the optional noisy headwind resistance unit.