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At customary working distances, a silver BD will produce harder shadows and brighter speculars. As such, it's a more difficult modifier to use, and a bit of a contradiction IMO. That light quality is roughly (very roughly) achievable with standard metal reflectors. I prefer a BD in white because it better fills the gap between a metal reflector and a medium softbox. You can give directionality and greater hardness to white beauty dishes with a grid - great combo.
For hard light (my fav), the great-looking results come from projector-style lighting fixtures like fresnels, but that's a different value proposition.
White BD as key for tabletop. Note smoothness of light, and nice shadow transitions: