The Mazda OEM Rubber Cargo Mat is worth every penny for 80 bucks. I would consider it a must have. It's about 12 pounds of solid rubber, a perfect fit, and keeps cargo from sliding around. Nothing wrong with the Weathertech, but this is OEM and about half the price (with shipping). It also adds another layer of sound deadening. Amazon has it for cheaper than the Mazda dealer.
I agree - the Mazda OEM rubber cargo mat is great. Things stay in place back there with that mat - nothing slides around.
I also like the Maxpider floormats for the front and rear - really sharp looking. The WeatherTech mats are nice as well, I just preferred the look of the Maxpider floormats.
I also purchased the OEM cargo cover for the back area. It was pricey (around $180) but I feel it's worth it for hiding cargo and gives the car a more upscale feel.