If you want your miniatures to have a nice look of shading or even a slightly dirty look this product is excellent. It's even great at quickly blending between two colors. This is best used when you have a large number of miniatures that need washes.
It's ink rather than a wash you can use slightly less to get a similar effect. It also takes a bit longer to dry.
It doesn't have the issue of being weaker like newer releases of similar products.