It IS just colored epoxy. It's not any old epoxy, but it's not super duper special, either.
Industrial Formulators Cold Cure, or west systems marine epoxy are both fish safe, but they don't recommend you use them for potable water tanks, because the liability concerns outweigh any extra sales they might get by serving that market.
As for fiberglass, yeah it can be a pain in the ass. I have a lot of experience with it though, so I don't see that bump in the road. costwise, how do you figure it's just as costly? for $300 you could get enough resin and Chopped Strand mat to completely line your tank with it (which is way overkill.)
Anyways, let's not derail the thread over this, Pond armor is a perfectly viable choice for lining a tank or a pond, I would just as soon use something less expensive, even if it's more of a PITA.