I bought it for my daughter along with other colors of Posca-type markers. While she was satisfied with the rest, she didn't like the black and blue ones, maybe because she expected more from these two colors.
In any case, the opinions and rating of a 4th-grade child (I asked her and wrote down what she told me) should be taken with caution, especially for consumables of this type. Personally, though, from the little I saw of them, I didn't find anything bad.
Happy drawings!