The Kaiser product is expensive but I would buy it it ever became available in the USA. I know someone who has it in Italy - It is reliable and precise. The food warming trays are anything but precise unfortunately.
But as indicated somewhere above one can set at food-warming plate at highest temperature and control it by an external control put before the mains cable and with a probe on the plate or in the bath.
Is that done here anyway? I do not remember much postings on this. But sometimes impressions are rather based on own conceptions, than on facts, so I might be wrong on this.