Im just starting to use backup temperature controls on my heat mats.
I have one hydro farm digital and and two zilla with a dial for setting the temperature.
The hydro farm is my favorite as the digital read out tells me the temperature at the probe at a glance- the sills ones require a separate thermometer for read out.

I've only had one small vinyl pillow type mat overheat, and it fortunately had a slab of stone over the glass to disperse the heat, and plenty of room for the snake to move away from the hot spot. (25%If or less of the floor.)

Heat mats are a supplement to my heating with incandescent lighting- I switch the bulb size up and down with the season, and when a bulb burns out I see it at morning or afternoon check.