I think the design was well thought out, and it looks like a wonderful accessory for the Weber Kettle. Controlling the heat from below, and getting radiant heat from the lid makes perfect sense. The same set-up might also work for biscuits or cornbread.
I guess I'm not that good scratch pizza baker. I have two Big Green Eggs, the kamado style ceramic pit, and have watched other people cook pizzas on them for 20+ years that are fantastic, breads too. In fact, at one EggFest event I was cooking next to the owner of our local Pappa Murphy's , and he cooked about 30 pizzas on a large BGE that day. He used their baking trays but on a stone. I finally changed from fresh dough to blind baked crusts which are easier for me to handle, plus I don't need a 500° fire.
I would say if you can make a good fresh crust that you are pleased with when baked in the oven...., by all means go for that Kettle Pizza Insert. The "live fire" or "brick oven" flavor is hard to beat.