Cast iron plate setter

Iron has a lower heat capacity than ceramic, meaning it heats up with less energy - holds less heat energy per unit weight.  It's also a better conductor.

What this tells me is you'll reach equilibrium faster with a cast iron plate setter.  When you shut down the fire, that heat will be released faster from the iron so you'll see a slower drop in temp than the ceramic, but the ceramic will dump more heat into the system in the long run after shutting down.

What does this mean?  I don't think you'll have a problem dropping the temp over a ceramic plate setter.  Why?   The mass of the egg is so great relative to the plate setter that mass will make a temp drop slow by itself.

The main difference is you'll get more heat through the iron plate setter than the ceramic, as the ceramic is a better insulator.  The shadow from the direct heat is all you really care about but I would think "bottom" cooking would be a bit faster with the iron.

Also, watch out - iron can break like ceramic.

Overall, I think the iron setter would be a good alternative as long as it is durable.

I have one and it works fine for indirect.  I got it initially because it is a little more durable than ceramic (though not impossible to break).

Nakedwhiz did a nice write-up on it:

http://www.nakedwhiz.com/productreviews/ibcps/castironps.htm