I have used quite a few different brands of purple shampoo, and as a hairdresser myself, find this to be the best one by far.
Sometimes, it can even be used on freshly bleached hair as a toner rather than applying another colour.
If it is used too much or left on a few minutes too long it can leave a bit of a purple hue behind which can easily be corrected by washing hair with a normal shampoo, but that aside, it definitely does its job well and at a reasonable price!
This is hands down the best purple shampoo on the market. Eliminates and golden or brassy tones you have in your hair inside 1-2 washes.
Tips: Mix it with your standard shampoo so it's not too overpowering
Make sure you don't leave it in your hair for too long as it may start to tint your hair a purple shade