Hello, I need some advice on going back to my natural hair colour please : )

Has anyone used Colour B4? It's meant to get rid of the dye. I'm a bit worried about using it... what if it messes up my hair?

I've been dyeing it with a semi permanent for about three years and want to go back to my natural colour and go short. I could just let it grow out a bit then cut it so short that only natural colour is left, but I have a style in mind already.

Any advice would be appreciated and Colour B4 reviews would be great. Thanks.