The spray in liners are pretty much the same product. The technician spraying is the difference on how it will turn out. This also goes for hot vs cold sprays as well. You want a hot spray liner with the surface at least prepped with scotch brite. Many dealers skip the scotch brite because it is manual labor and they will warranty it if it lifts- by applying more spray liner that is not bonded to the un-prepped surface. You get what you pay for. As a weekend home depot rig it wont matter over the life of the truck if it is mis-applied.
As far as tonneau covers the diamondback is the end all be all of bed covers strong enough to put another car on it. It will not dent without hitting it with a ball peen hammer. I am not a fan of the black finish on aluminum as they all come up over time. Save the $$ for the black finish aluminum and go with natural.
I recently went with a Undercover Flex hard aluminum foldable. I dont regret it but understand that it can sustain hail damage when the truck sustains other hail damage. Weight load capacity is 300#'s.