It works if you work it.

Tips for using this product effectively:
Use more than you think you need - your hair can't be too saturated.
Wrap your head in plastic and leave the product on for at least 1 hour.
Sit somewhere warm. Simple chemistry will tell you that most chemical reactions work slower in colder temps.
Follow the rinsing instructions. The more you shampoo it during the initial rinse, the better your results.

Following the aforementioned steps, I was able to take my hair from "midnight merlot" (Dark Plum) to light red, which was light enough to then go blonde with 2 applications of 20 volume bleach. If you know anything about hair, you know this product is basically a miracle.

Granted, it's near $20 a bottle, but the same process at a salon would have cost me nearly $100 so it's totally worth it.

Cons; It stinks! It doesn't smell like ammonia because it's not a bleach ( it contains Hydrosulfite which rapidly reduces the dye molecule, and washes away with shampoo) but you will smell the chemical process for a few days after. I still think it's worth it.

Literally a life saver.

I was sceptical. My hair is hip-length and I've been colouring it monthly, for well over a decade. This product, in one application, stripped my hair of a decade worth or red & black hair dyes - in less than an hour!
And to my surprise there was no damage, my hair actually felt better after the treatment.

Granted, it smells.... unique. And not in a good way, but it's not nearly as intolerable as hair bleach!
The best part about this product, I was able to colour my hair the same day.

The science behind it is amazing!

I have been dying my hair every color on the shelf for years at home. I bleached my hair approximately 4 months ago after being a violet head and it came out a very brassy orange blonde. I used my go to cover up (jet black) a week after. I have been trying for about a month and a half now to find a way to lighten my hair without the ammonia / bleach again. Thanks to Color Oops Extra Strength, my hair came out a lighter shade brown, not too light at all. At the moment I am debating re dying I like the turnout.

I bought this product to remove a dark purple red i had been wearing in my hair for over a year. I thought for a drugstore brand that it would remove it a bit but not fully with its price. Well i was wrong! I saturated my very long hair with just one bottle because it was so fluid to apple. I left it in for 30 mins (it says 20 but i thought my hair is usually resistant to any kind of lightening products so i might need an extra 10) Afterwards i scrubbed, rinsed fully twice with a good shampoo and now it's a nice dirty blond colour with no reds what so ever. .I can now apply the colour I really want! Needless to say I'm really happy with this product.