My friend had one of the Weber ones, and said it wasn't worth the hassle.How do those pizza stones fare on the Webber bbq?
His biggest issue was getting an even cook. In an Ooni or a standard home oven, the heat is more evenly distributed. With the Weber, he could get it really hot, but the stone would cremate the base leaving the topping underdone. To combat this, you obviously can run the Weber at a lower temp, but then you may as well use an oven. I did look at getting a stone, as my Weber kettle is genuinely one of the best things I have purchased in the last few years, but after seeing (and tasting) the results, I decided to go a different way.
But, that's just one persons opinion. Maybe with a bit of experimentation, you could get a better end product.