I'd definitely prefer polycarbonate over aluminum or any metal in some situations. For instance, I'm fine with the Canon RP using a plastic body. It's lighter and provides better bump protection.Just out of curiosity, I was doing some research on polycarbonate, and came across this forum discussion regarding the use of aluminum vs polycarbonate for "bot wars" construction, and polycarbonate seems to be the clear recommendation. Not sure how that translates to lens mounts, but if it is better at surviving a robot-to-robot collision, then maybe there is some truth to it
I recommend polycarbonate. Any mechanism extending out of our bumpers (within volume constraints of course) are polycarbonate. Polycarbonate rarely cracks or breaks on impact in standard conditions. The only time we have ever cracked polycarbonate was in 2015 with our polycarbonate tote intake...www.chiefdelphi.com
I just always imagine tiny little black plastic shavings that get onto the sensor from the continuous mount and unmount of plastic mount lenses. But who knows, maybe metal on metal creates more shavings, and there is actually more risk of scratching your sensor when cleaning.
I think there were some Canon rebels where both the camera and the kit lens used plastic mounts. I wonder how well they've held up.