The bobeches are bent glass, not plain flat glass pieces. They can catch and hold the melted wax effectively.
The inside hole edges and outside edges are finished with a rounded bead, so there are no sharp edges to worry about.
If you use tall candles, these are just what you need. They catch the drips from the candles and are easy to clear the wax off.
Save you work cleaning wax off your table. They really add a touch of care and elegance.