I have used it before--and it had the same result as bleach--meaning, it did not remove just the color from my unbleached hair--it stripped it...to a bad orangey blonde, and it was really muddled--different parts of my hair were darker, others were lighter. Bad. But this was maybe 8 or so years ago. Perhaps it's improved.
Don't know if it's any better from your hair than bleach, but if you are looking to strip your hair so you can color it again it might be ok.

This is an old post but I just joined so... to answer the question on hair color remover, I love it. It works though only on permanent color It does work on demi never tried it on semi package says not too. My experience as a professional I have only used Rusk. I swear it like dissolves the color away. My clients was a deep burgandy and wanted a platinum blonde and I used remover and one round of leach with low volume per. results were great. But most importantly her hair felt great after. Not so in my experience if you use bleach only. My experience with effesol was the same it's a nasty little product. Even in beauty school they advise against it. Very harsh on the hair.