Ruin your tub.
Its just soap, without scent, and very fine black grit or charcoal.  Its suppose to absorb and lift out toxins but how does it absorb in water?  Its like rubbing yourself with a wet Bounty Paper towel, sure it was absorbent until it got wet right?  Will leave a fine grey film on your tub, tile, and shower curtain that builds over time.  Noticed zero difference over the cheapo store bought soap other than my tub looks disgusting after a week, doesnt come out of grout of course which is awesome.
Rating: 2 stars