I currently use several seachem products but I've never used purigen. So there is little I can do to answer your question other than to say ...all of my experience with sea chem products has been good.
The following info is from seachems web site:
Purigen™ is a premium synthetic adsorbent that is unlike any other filtration product. It is not a mixture of ion exchangers or adsorbents, but a unique macro-porous synthetic polymer that removes soluble and insoluble impurities from water at a rate and capacity that exceeds all others, even HyperSorb™, by over 500%. Purigen™; removes proteins, nitrites and nitrates, ammonia, and a broad spectrum of organics, yet its impact on trace elements is minimal. It significantly raises redox. It polishes water to unparalleled clarity. Like HyperSorb™, Purigen™ darkens progressively as it exhausts, and is easily renewed by treating with household bleach. A 100 mL bag of Purigen™ purifies and polishes up to 100 gallons of water for up to six months. Purigen™ is designed for both marine and freshwater use.