"Crystal" and "Mud" are two words that don't normally collocate, so a product named "Crystal Mud" is already intriguing at the linguistic level.
The short summary: you know those grass jelly drinks? Well, if you've ever wondered what it would be like to bathe in grass jelly, this is what you want to try. I understand this is the same stuff you see used for some indoor plants as well (for people who like plants but who prefer the clean look of jelly over soil - something I could never understand).
The 5 satchets you get per box won't quite fill your bathtub - you won't be bathing in jello (although that would be interesting ...) but they will create enough swirling jelly bits to make for a strange experience.
I found it somewhat disconcerting (I don't like things floating in the my bath with me), but I did think the jelly bits made for a fascinating photograph (which is the main point of this post). The photo was taken in candlelight, wide open at f1.8, and about 1/30, then contrast was pushed in photoshop.