Is the miracle thaw safe?
It's certainly safe in terms of food contact. See How does a Miracle Thaw work? - it's really just a sheet of metal. It's not very much different from just putting your food on a baking sheet. Just be sure to clean it between uses as you would with anything else that touched raw meat.

However, you do still have to be careful about general food safety: it's not safe to leave meat in the danger zone (40 to 140°F) for more than a couple hours. The miracle thaw speeds things along, but it doesn't change that. So if it makes your meat thaw enough in half an hour, awesome. If it still takes 6 hours, you need to find another safe thawing method to use instead.