This clear double dice d10 has a small red d10 inside of a larger transparent d10. With double dice you can roll a percentile with a single die -- because the double dice is actually two dice in one. The larger transparent d10 is substantially bigger than standard dice size, while the smaller interior die is smaller than standard. Double dice are an increasingly popular way of handling percentile rolls, though of course just rolling your percentile dice, or two d10s of different colors, works just as well.
Without question the double dice are an easier to roll and read solution than the d100, though perhaps not quite as cool.