It appears as if the intention is to grill the pizza, not bake it, as the pic shows no stone. Grilling pizza doesn't take much, certainly not a $100 stacker.
This does not solve the single biggest problem I have with making pizza on the kettle, which is browning the top. The solution involves either getting the pizza as close to the lid as possible, or placing another stone above the pie. This stacker, if anything increases the distance between the pie and the lid. I guess if it holds high enough heat it might all work, but I'm far from sold.