Yup, this and other products are definitely a scam designed to exploit people who know little about thermo. When you turn your comp off, your CPU will never get hotter than the temp it was at when on. Where is the heat coming from to make it hotter? There is no current going through the CPU...
Besides, the operating temp and storage temp specs of a CPU are very different... you can have a CPU at 100°C if it's not running. So even if the CPU was somehow magically getting hotter after being turned off, it could get up to 100°C without damage.