If I'm remembering correctly, the X-Dual Pro came out first, and when the Pro One (16x19) came out soon after, the X-Dual Pro was quickly renamed the Pro One 18x20. I could be misremembering – Donnay's release and marketing schemes always seemed confusing to me – but I hit with both X-Dual Pro and Pro One 18x20 and couldn't see or feel any difference between them.