I'm almost convinced that one could splash cold water on thick, hot cordierite and it wouldn't crack. It is very thermal shock resistant and continues to impress. I have been very happy with the cordierite shelf I ordered. I have used various pizza stones and tiles in the past with a mix of disappointment and trepidation over the cracking issue, and in some cases a sticking issue. In my case, both tiles in a wood-burning grill and a Pampered Chef pizza stone in an electric oven have failed spectacularly. Regardless of stone/shelf/tile brand, the best advice I have is to buy it at least 0.625" thick (although the tiles I used that cracked were 0.625"), preferably 0.75" thick. It takes a little longer to heat up than a 0.375" or 0.5" thick stone, but it will save you from a lot of headaches in the future.
I'm a perforated disk kind of guy, and I haven't stopped using the cordierite shelf since its first use three weeks ago. Just for reference, I paid just under $20 for the 16" x 16" x 0.75" shelf, an additional $6 packing fee, and $15.88 for shipping. Sheffield Pottery no longer carries the 0.75" in square shapes. They have either 0.625" or 1.0" thicknesses.