It's good. Seriously, it contains just about everything someone getting into spearfishing needs to know in an excellently arranged and understandable manner.
My only issue is that I feel it really should cover triggerless (polespear & Hawaiian sling) spearfishing as well. I expect they'll get around to adding triggerless content as time goes on as they sell some great polespears and a lot of the information in the Academy section is applicable to anyone using a polespear or a sling. Still, a little dedicated polespear and sling content would be a welcome addition.
Definitely the Neptonics Spearfishing Academy pages deserve to be bookmarked as your go to reference for spearfishing information.