The jettrim side mats are designed to replace the oem side mat material. I just got a set for mine, the ones that work with the oem rubber caps. Since the side mat material is in great shape, I'm leaving those and adding just the bottom mat. When the time comes to replace the side mats I'll remove the oem so tray width isn't reduced like user mentioned.
This is a personal preference but I really like the rib option for the tray mat. The ribs give you added traction and padding, and look cool as well.