I've recently installed the Bak Revolver X2. I liked the solid roll function and that said roll rests on top of the bed and not below it. Installation is finicky to get everything lined up right. Its taken awhile for my side seals to sit down, so I got a heat gun and expedited the process. We'll see how it holds up in the next rain storm; my last storm did have more then a few drips to be sure.
It looks good, and my cargo is more secure due to the solid aluminum roll structure under the canvas, however at this point I'm not sure I'd buy another one.