So provided you use your MR D as recommended, there is no health risk. It is not the type of cooking where you need to take a peek as it is virtually impossible to overcook the food. They are commonly used by those in the sailing fraternity, as they can never be sure what the weather will be like when they want to prepare a meal if they are at sea, so they prepare it when the conditions are calm to eat later.
You can use the MR D for normal cooking as well so it has a double purpose if you are concerned about the space it takes up as could take the place of a large pot or pan or two.
I was a Microbiologist in one of my previous lives and have investigated a significant number of food poisoning outbreaks. As the food is at boiling point when the lid is put on and is packed into the insulating bag there is minimal risk of food poisoning provided your preparation methods are hygenic and you do NOT PEEK AT IT until you are about to eat the meal.
No problem then unless of course the initial ingredients were contaminated with a bacteria that produces heat resistant toxins or heat resistant bacterial spores, but this is a problem no matter what type of cooking method you are using. So please always think hygene in buying, storing and preparation of foodstuffs no matter how you are going to cook them..
