Spend the money for a better one if you are going to use it on the grill. Or find a place that sells 1" thick fire bricks and get a bunch of them to form the area you want to put the pizza down. The thin ceramic stones tend to crack and shatter when exposed to the high direct heat of the coals or burners in a grill. If you can rig your grill to only provide indirect heat around the stone and not too close to it, you might get by with the thinner, cheaper ones.
I bought the volcanic stone just for the grill after blowing up a few lesser grade ones.
Thunder.Gerbil wrote: