These , and other items for like purpose , were pretty much last used by folks migrating around for work & for having a portable "microwave oven" (no fire to build , etc.) while traveling/camping-out & for other temporary functions in areas where house current was available , as far as I know .
Even through the 1940's , gas , coal & woodfire were the dominant form for stoves .
These little units must have caught the eye of traveling families with hongry youngins' , in their day !