Just getting this from the link you posted, but I think the metallic option just has them spreading metallic flakes in the solid epoxy coating before it dries. I think it would add some traction (maybe -- check on that) and might have a cool look. They might put an additional clear coat on top of the flakes. The regular sounds like it might be smoother and more reflective. The part that makes me think this is that the regular solid epoxy says "without any broadcast medium..."