I understand that it halachically permissible on Shabbos to place dry, already cooked food (such as leftovers from the fridge) on a warming tray so that it will get warm.
However, there are several halachic restrictions I've heard (I'm not sure if all are universally agreed upon): for example, that the warmer can't be capable of heating food to yad soledes bo, or that the warmer not have an adjustable dial, or at least that the dial is removed.
Are there warmers that are halachically approved for use on Shabbos, or which are in practice widely used by Shabbos-observant Jews for this purpose? Please share the make and model of halachically-compliant warmers.
I ask because, regarding the warming trays on the market, there is ambiguity about the purpose of these trays. If they are used on Friday night to keep food warm, it doesn't matter how hot they get if they were put on the tray before Shabbos began, while if they are used on Saturday to warm up cold food, the above restrictions may apply. For example, I have seen warming trays advertised for use on Shabbos for which the reviews say they get the food extremely hot, suggesting they are not suitable for Saturday use.