Look at the thickness of the unit, as also denoted by the weight. It is an insulating refractory, and as such stores minimal heat for the mass. It works great for fireplaces, but for a retained heat cooking unit it is mediocre at best. If they thinned it down and lined it with firebrick, they would have something, since the material is also structural. From their website:
"Made of the same proprietary insulating materials as our fireplaces, the wood fired outdoor oven can sustain temperatures of over 900 degrees Fahrenheit."