Here are some of the commercial thermal cookers I’ve purchased and have an opinion on.
The Thermos/Nissan brand have been the best quality brand of thermal cooker I own. I have a Shuttle Chef 3L version and 4.5L RPA4500S. They use a vacuum flask as the insulator which is superior to other outer containers that use a foam core or other insulator.
The stainless steel innerpots are of a thick gage steel and well made. The bottom of the RPA4500S innerpot is stainless stell. On the CC4500S model the bottom is clad with aluminum.