On the front:
Some simple, somewhat abstract, somewhat minimal illustration that captures gait training with the Spartan, or the spirit of it. People who use the Spartan are the aggressive type that are not afraid of hard work, so let it be an aggressive image that matches the product's name. The image can go directly in the center.
Below the image, simply the name "SPARTAN"
Below SPARTAN, have "A New Kind of Gait Trainer"
At the top of the front, the logo (use the one with no tagline).
On the back, an image of the Spartan itself, centered, with the words below it: "MEET YOUR BODY'S POTENTIAL"
For the Spartan image, use the PNF file attached ("SPTN"). Keep the image very high quality, but trim away the boarded and excess stuff that isn't the pair of devices.