Ease of Iron Supplementation: It's popular because you can easily get iron just by putting a iron egg in when boiling water. Impact on Taste: Some users report a slight metallic taste in the water after use, but it's not bothersome. Need for Care: It's pointed out that it rusts easily if not dried thoroughly after use, so care is needed in storage. Excerpts from User Reviews: "Bought it for my child's iron intake. My child, who is sensitive to taste, doesn't even notice it." "I use it by putting it in boiling water for about 5 minutes. I can taste a little iron, but it's not a problem." "It rusts if it's not dried properly after use, so I store it with a desiccant." Overall, it's highly rated for its ease of iron supplementation, but care is needed in cleaning and storage after use. The Iron Egg Thin Type Nambu Ironware IRONCRAFT Black Beans Glossy Thin Type Iron Supplementation New and unused Nambu Ironcraft Nambu Ironware IRONCRAFT The Iron Egg Thin Type Dishwasher and microwave safe: No You can supplement iron just by putting this iron egg in a kettle and boiling water. You can use it not only for hot water but also for "removing sand from clams," "coloring nukazuke (fermented rice bran pickles)," and "adding gloss to black beans" during cooking. Immediate purchase & silent purchase are welcome! Please buy with confidence!