Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Worst product ever - quickly grinds itself smooth

After 3-5 minutes of grinding dried tea leaves into powder, the mortar and pestle became 100% useless. What they dont tell you is that the "rough" unfinished porcelain (which is supposed to help grind up items), quickly rubs itself completely smooth. After only one partial use, its ready for the trash, as the inside is like glass. The idea of this device is that it MUST be rough inside to help grind items up. Dont waste your time or $$ on this one. The porcelain seems to be very soft as well. The pestle is already rubbed flat on one side after 5 minutes of use. I never review products but this one made me so mad I had to inform other!