They're a pleasing design but that's about it. The purpose of a coaster is to stop the surface (table) from getting wet/watermarked. When these coasters get wet (through normal use) they warp. If the glass is light enough (e.g. an almost empty stemmed wine glass) it topples because the coaster is no longer flat and spills the remaining contents on the surface you're trying to protect. Potential safety hazard if the glass were to break… Death by coaster.