I've never seen plastic screws used on a BP&W. That could be because we all use Aluminium tanks here, so scratching isn't an issue... but then again, I've never noticed an ali tank that was obviously scratched by the screws...
I really liked the divegearexpress website. Very professional and informative. With regards to the plastic screw...to be fair to them, they do say:
Quote:
Without the assembly screws, when the BCD is taken off a single tank the wing will hang loose on the cam straps. Note that this function is just cosmetic, some people prefer to omit the assembly screws and this does not cause a problem.
I read that to mean that these screws are for use when the BP&W are only secured via threading the camband through the wing and backplate. The screws are not 'load bearing' and only exist for holding the kit together when a tank is not attached (out of the water). They are probably fine for that task. At $2.50, rather than $14 for the SS bolts, they'd make reasonable sense.