I have a sapphire halo from the June batch. It has the polished base and exterior with a matte/frosted texture on the inside of the dish. I have used it at 600F for about 3 months. I have cleaned the dish using oxiclean, isopropyl, grain alcohol, and hot water/steam, and have run it through an ultrasonic cleaner. I have never heat cleaned it. No cracks yet (knock on wood)
I use the washer on top of the heater. This is tightened just to the point that the heater stops moving. The dish/retainer nut are tightened only to the point the dish stops turning.