Great product. I use NO 27 Silver every 3 or 4 weeks. It lasts very well and always comes out the perfect shade of silver. So long as you make the effort to maintain your colour with toner shampoos, it will stay looking vibrant and perfectly silver. I have also found that since it is only semi-permanent, it does not damage my (already very bleached!) hair at all, so I have no qualms about leaving it on for the full 30 minutes. It does dry my hair out a bit, but that can be instantly remedied with a good conditioner. The product design is also very appealing. I have very long hair (to my thighs!) and need at least 3 bottles per application every 3/4 weeks, but since the dye is so affordable, I'm very happy to spend the money needed on something that works so well.