Thermal cookers are a good thing. They cook with very little energy so save money.
They will also keep food hot for a long time. Some up to 12 hours. Its a neat way of cooking and can come in handy during power outages.
To make a thermal cooker check out katzcradul”s video. To see how the different ones work check out 3stepsorg’s video
How to Make a Thermal Cooker