I used this product many years ago when my hair was shoulder length and it worked great for me.
What I remember is that you need to check your hair to see if it is the correct color otherwise you will get a not so nice color. :-) I learned that and always took an extra 5 minutes to get the best color, especially at the roots.
Always use good conditioners afterwards.
If you cannot afford a hairdresser and you have someone that can help you, this is a great product.
Just remember to take extra care of your hair afterwards.