I have no experience with diamondback covers but experienced a few other types of covers during dive trips on a buddy's truck. For my use, I don't like solid or folding covers because accessing gear in the front of the box is a PITA.
On my buddy's F150, the folding cover was a two-man job or two-handed for one person while standing on the ground. My Roll N Lock is always a one-person operation.
Also, the folding cover collected water and became very heavy to open and close, especially during the winter. I supposed there's not too much risk of freezing solid in Florida.
I'm on my second Roll N Lock and have used them on my trucks since 2007. They require no effort to fully or partially open, can be locked partially opened, and are great for security when closed.
I have no experience with realtruck.com which now owns Roll N Lock.
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They are suitable for my needs.