Jonathan that article by Randy is 9 years old, whereas the science is the same I am sure manufacturing processes and binders have progressed. You can also find articles on Iron poisoning from GFO and it's effect and contribution to pinched mantel syndrome in Clams, but yet a lot of people still use GFO.
True the article is old, but the solubility of aluminum oxide in seawater hasn't changed. Perhaps they are washing them better now, however.
It is probably Ok to use. I have been using up small amounts of various types of aluminum oxide binders with my GFO since I have tons of it around from those early tests. At very low doses, I do not see a problem.
But if folks do see any corals closing up, especially leathers, then that may well be the cause, and I'd stop using the product.
I'm not sure what iron tox articles you may have seen, but I'd be interested in seeing them. I can certainly believe that if fine particles of GFO are released to the tank, there may be a concern. I have seen some unpublished studies that show such release (not proven to be particulates, but I think it likely), and that is one reason i prefer to use GFO in a nontumbling application.
That said, I think many of the reported issues when using GFO are from phosphate going too low or dropping too fast, not from the iron itself. Lots of people dose iron and I've not see folks report problems from that.
FWIW, I do not know the chemistry behind this Brightwell product.