If you grill or use the oven a lot, I believe this product is a must. It saves you money as you won't need to use aluminum foil, and using these instead of placing food directly on the grill, will also keep the grill cleaner.
They are even dishwasher safe which make it even easier to clean. The only things you need to be careful about is that they can't be used with temperatures too high (over 500) and too close open flames (if the fire actually touch them, they will melt!).
They do the job as they should, so 5 stars!