I can't speak to which is better as I've never used a ci or metal sheet. But some people swear by ci/metal.
Summary from the linked review:
Verdict: It's a keeper. Definite keeper.
Bonus points: on top of its clear thermal superiority, it's also far more durable (how many of you have cracked a pizza stone, raise your hands?).
Big Steel Keg, WSM, OTG, PBC, Super Fast and Accurate Blue Splash-Proof Thermapen