I have a Vision Pro that came with the lava stone heat deflector and I like it, I've had no trouble with it and I've been using it year round since June 2012. I recently noticed the Vision site said they are selling deflectors separately again. I still use a cookie sheet placed on the firebowl edge, above the stone but below the grill to prevent burning. I smoke a lot of whole legs and shoulders so the edges of these big pieces of meat need a larger area of protection than the stone alone gives.
I'm jealous of the ¼" steel. N8man has a steel plate in one of his vertical metal smokers and he says that thing works beautifully to regulate and distribute heat and lasts forever. Don't remember how thick it is, I think it was some kind of agricultural or industrial saw blade. I'd love to get my hands on one this summer, I'm planning to bring an old bullet smoker to life and I'd rather have a thick steel plate deflector than a water pan. I'll use stone if I can't find the right piece of metal.