I think it's pretty cool. the fact that it's an option is the big thing. you don't need to take it.
some pros; easier to get at stuff in the box, easier to clean out sand/debris without catching in the seam, you have a *sturdy* spot to grab when using the step in the box, still can be used like a traditional one for long loads... I think it's pretty good.
any negatives are just speculation of future issues. that comes with every new thing. I think it's a good option and will have a decent take rate. more so than the rambox as it doesn't "take anything away" from the bed.