Not so far. We had a really bad winter here in ireland and i use heat mats on the outside on the bottom of my tanks, and i had no problems at all, as long as it is on the outside of your tank i don't think it's anything to worry about. But you can put the heat mat on the side wall on the outside as well.
I'm new to beardies also, but what I did as a compromise between sand and tile, is put textured tile down as flooring, and gave Puff a small sandbox. He kicks the sand around, but its easy to clean up, and he gets the best of both worlds!
Nice idea! Don't know if I will definitely be changing his substrate yet (I guess it's a matter of opinion). Everyone I know uses sand (children's play sand, not regular sand) and the guy at the pet shop said chance of it causing gut impaction is slim. But I will definitely take all of the advice on board.