Personally I prefer paper towels, slate, tile, non adhesive shelf liner, ect. Nothing small enough for the reptile to swallow.
For dessert and other high temp animals, I like slate and tile, for tropical ones like my crested gecko, paper towels.
No fear of anyone swallowing anything and becoming impacted, and easy to see if something is off in their poop.
Granted I have seen some amazing living vivs done for several different kinds of animals, I don't have a problem there as long as its an adult animal who could handle accidentally eating a bit of the substrate better then a wee baby. Most people who do living vivis that I have seen feed any live feeders out side of the tank as well to help keep down the risk of substrate eating on accident. .
"And 5, very important 5... Don't let me eat pears.. I HATE PEARS."