The ones that I installed went in the concrete walk and steps from the kitchen door to the end of the garage. We put down insulation, rebar on stands, then the heat mats.
I have wondered a couple of times if the ones that lay on top of the concrete might have been a better choice.
The in concrete ones are not inexpensive.
The factor for me was the house eve always dripped and put water on the walkway which is shaded most of the day so the ice would build up considerably sometimes. I have also added gutters during the exterior redo we have done the last few years which have reduced the ice build up some.
This is what I put in almost 3 years ago;
When in use they pull just about 6Kw so at our current 22 cents/kwh they cost me a$1.32 per hour to run,
after shoveling or plowing/blowing it usually takes 3-5 hours to finish clearing the 30 ft section. Today I turned them on about 10AM and promptly forgot about them till 4 PM by which time they had not only melted the ice but (evaporated) all the water too bone dry. So $8.00 have a nice safe walk.
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I do have 3 1/2" of concrete over mine, less concrete and more insulation might have been a better idea but I have run a 10,000 tractor up on mine when using the work basket to clean pine needles out of the gutter guards.