i know on the youtube videos snakebyte they actually use coconut fibre for them to lay there eggs in so cant see a problem.
but my opinion would be use what everyone else uses on here
i use newspaper as easy to clean etc but thats not fancy i have had a male get prolapse hemi penis from sand getting stuck in the shaft when breeding so have always stuck to newspaper and tiles after my issue.
but i know people that have used sand for years with no problems at all
i did use rocks as well at one point looked very cool but was hard to clean out having to pull them out all the time etc.
when choosing the subtrate remember whats easy to clean i recommend artificial grass in a show tank