Floyd- My information came from in person discussions with a Seachem rep and the information available from them. I'm not saying to not use Purigen, but let's be clear on one thing. Any supposed benefits over carbon relative to LLD/HITH is pure speculation. In our setups (40 or so planted now), we run no carbon or purigen. If you are dosing ferts and running purigen, there's a bit of contradiction to me.
From Seachem's site- "Purigen® generally ignores simple elemental compounds, having an extreme affinity for nitrogenous organics. The primary source of nitrogenous compounds in an aquarium is waste. Fish, corals, even plants produce nitrogenous waste. Purigen® removes that waste faster and more completely than anything else on the market."
Adding nitrogenous compounds to fertilize plants while running purigen seems a bit "round and round" to me. Not to mention that theoretically at least, you can starve your biofilter by removing too much. JMO
In a fish only tank, I don't see a reason (beyond my own cheapness) to not run it. My point, if I have one, is that chemical media IS NOT a requirement for a healthy tank. Say what you will, I have proof in the form of many tanks with all variety of stocking from SA to Rift lake to Reef.