Cabela's has the same one as sportsmansguide slightly cheaper. Two sizes. Reviews online @ cabela's.
It isn't purported to be a heavy plate safe, study of the photos shows it is a formed metal clamshell in light gauge steel. The cable is rated 1500 pounds but is not cut resistant. It does cost less than the Simplex lock alone, is portable, TSA rated, and fits in briefcases, luggage, etc.
TUFFY offers lots of alternate lockboxes for Jeeps, utility contractors, LEO, and custom order. They have dozens of sizes, designs and styles in coordinating interior colors.
If there were any criteria I would apply, it should be secure, easy to use, not telegraph what the driver's up to, and unnoticeable. A key fob door lock system would be a desireable addition - you'd be acting like any other suburbanite locking up the car.