I purchased a 2-pack of these salt tiles on Amazon.
Here are my thoughts:
Shipping/Receiving - Although they came bubble wrapped, the corners were still worn off from excessive "handling." One of them clearly had a severe crack running through the tile. As I suspected, when slowly warming it up the first time, the cracked one exploded in the oven. Of course, Amazon is awesome and sent me a replacement.
Tempering - If you're going to use them to cook on, then you have to temper them to heat. This means the first time you warm them, you have to do so VERY slowly. The process I read about and used was to put them in your oven, set the oven at 200 degrees...wait 30 min...raise the oven by 25 degrees or so every 20-30 minutes until the oven gets to 500. You only need to do this the first time.
Cooking - I've mostly tried to use them on the grill. The idea is it's fun to use them as a surface to grill/cook food on...and you get a nice slightly salty flavor on the food. The biggest drawback I've found is the blocks take a really long time to heat up...so where as it only takes 15 minutes for my grill to get to 500 degrees, it would take the salt block in the grill 30+ minutes. I always feel like I'm wasting too much fuel when using these. I notice the description on the "two small brick" write-up says they warm up in less time than this (and in a 350 degree oven), but I heartily disagree.
The steak I cooked on them was tasty, but it was also pretty salty. If you're sensitive to salt flavor, then you're going to disagree with the "slightly salty flavor" description and consider it "really pretty salty".
All in all, I say it's a gimmick, but still a pretty fun gimmick. I haven't used them to serve cheese/appetizers on yet, but they are pretty.