Firebrick, even thinner firebrick splits, takes a tremendous amount of energy to pre-heat. In a proprane grill, that translates into a lot of propane. In a home oven, that usually transfers into a couple hours pre-heat.
Firebrick also lacks the necessary conductivity to give you fast bakes in a 550 home oven. For 550, 1/2" steel is your best bet. Using 1/2" steel plate in combination with the broiler, the bottom of the pizza and the top of the pizza will both cook in a very fast time frame. For NY style pizza, this fast time frame makes for the best pies.
Steel is not ideal for a bottom heat scenario grill, though, because there is no broiler to speed up the top bake. In a grill, you want a less conductive material. Quarry tiles have a low conductivity, but may not be durable in a grill environment. Fibrament can perform well in this setting. If you're willing to spend the time and the money for fuel for the pre-heat, firebrick is a durable option for the grill.