It’s a type of organic carbon, in the form of marine sourced biopolymers.
What it does is, bind excess metals/nutrients, make your tank water incredibly clear and eliminate detritus.
The reviews I read were mostly very positive. I can’t think of a reason why it hasn’t become more popular, except for cost.
I plan to use it in combination with Plus-NP and All for Reef, also made by Tropic Marin.