I own 6 of these! They are visually stunning, seamless and do not leak. I feel the best colour to order is the GOLD as the sparkles inside are a variety of sizes and shapes which allow them to settle at different rates making the use of it easier to explain to children when using it for the purposes of teaching what happens in our bodies when dysregulated. I found with the green one for example, there appears to be only 1 kind of sparkle inside which I feel makes it harder to visually see the sparkle settling.