I have Line-X on my current truck and had it on my last. That being said, I don't haul that much that would scratch it so it is probably a waste. I also have a rubber mat in my current truck. I'm not sure I'd buy Line-X if I bought a truck without it. You can always add it later. I've also used a bed rug on one truck and I liked it alot.
http://www.bedrug.com/products/bed-liners/bed-rug.html It made a flat floor which was nice for sleeping on.
Protecting the paint that you can't see because you cover it up seems nonsensical to me.