Pertaining to the gas fire tables, I would not allow marshmallows to be cooked on it. It will end up dripping on the glass beads or lava rock and burn/catch fire. These are also bug attractants, we notice a lot of bugs flying into the fire and burning up so you'd be melting your marshmallows over a bed of burning bugs!
The glass rings on our tables are great. It still puts off plenty of heat, but helps contain the flames on a breezy night.