Does anyone know of a kosher hot plate that can be safely left on for the duration of Shabbos, Yom Tov, or a 3 day Shabbos and Yom Tov and will not become a fire hazard?
Every product should be and can be a kosher product.
Bringing any product to market requires competent halachic supervision:
http://www.kosherimage.com/approval.html
Gaining rabbinic approval for a product is critical:
http://www.aish.com/sh/l/48970106.html
There is a huge difference between a product that is manufactured without halachic supervision and a product that is manufactured with proper, competent, orthodox halachic supervision.