In a bold move, they metallized a rubber sword accessory. Wouldn't it crinkle on the first flex? I admire their gumption.
Depending on the rubber stiffness, vacuum metalizing is so thin that with minimal bending, it will only get micro cracks, that are barley noticeable.
For the American version of Masked Rider we had Count Dregon's helmet metalized and it was made of a urethane rubber. Even after a season of shooting it still looked pretty good. You could clearly see where it was being bent (to put it on, you had to flex it, hence the reason for it being rubber) but it held up much better than I expected.
Side note: The chest and belt plate where also vacuum metalized and I think the gauntlet pieces where fabricated in aluminum and polished.