Plant heat mats.

I know that under heating for houseplants by way of a heat mat is a genuine thing. My question is, are heat mats designed for plants pretty much the same as under substrate heat mats that you can get for reptile enclosures?

We have a snake and as it got bigger we've upgraded the size of the heat mat for it. The old ones, just the right size for under a plant pot, are just stored away in a spare bedroom.

I was thinking maybe of doing something with them, whether it's putting a plant on them, or sitting trays of water on them to help with humidity.

Thoughts?

 

Possibly useable for seed germination I would have thought, I cant see the advantage for adult plants unless in unheated places.
They would perhaps need a thermostat to stop them overheating?

 

I have one of these:

bought for overwintering some hoya babies last winter. I placed heating mat on the bottom of the transparent box, then plants were on the tray above the mat. Roots of plants died.
This year I placed the mat sideways in the box just to work as radiator, I keep it on minimum, it maintains about +19+20C temperature inside the box.