Eating this stuff would be about as bad as eating any regular cat litter that uses Fuller's earth as the primary absorbent. The extra special ingredient (powdered quartz) is effectively nontoxic when ingested. The real issue is the chronic exposure to very fine silica dust.
Edit: to clarify, I do not believe that it would be safe for humans or animals to use this as cat litter. Just realized that this comment might have been taken as a "well akshually it's fine." It is not fine, silicosis is a dreadful condition.