Does matrix so silver shampoo really work?

and if it does do a good job of keeping the brass tone out of my blonde then how often should i use it?Does matrix so silver shampoo really work?
I've never used the Matrix brand but I have used several other shampoos that make the same claims. I have platinum blond hair and find it difficult to keep it from getting yellowish over time but these shampoos are a lifesaver. I use one from Joico about once a week. I apply it, let it sit on my hair for a minute or so and then rinse. It keeps my hair shiny and platinum without drying. Be careful not to use it too much because it can deposit purple or blue tones on the hair.