Looks like a fad.
Wont be part of my usual grill offering.
Yeah, they work, but don't do anything special.
You can get the same taste with a cast iron skillet and a salt shaker.
Seriously, an old fashioned way of doing much the same thing is to take a cast iron skillet, no oil, put a thin layer of kosher or other large grain salt in it, and get it blazing hot.
Slap you meat in it, and cook away. Steaks done this way are particularly tasty. If the skillet is seriously hot, all the juice will be sealed in.
same with fish, forms a nice crust, fish stays moist.