This works very well. It is important to wear gloves and this can make it a bit inconvenient. But, the results are good and do not make it seem obvious the colour has changed. It can be used to create a gradual darkening of hairs. I like to keep some grey hairs and this helps me do that successfully. There is no bad odor. I do recommend shaking the bottle well and being careful squeezing because it might come out too fast and be wasted. It is possible to leave it in the hair for more than the recommended time to have a stronger absorbtion and stronger effect. However, be aware that it can stain, so use dark materials when drying hair or using while wearing clothes.