spa chemicals are a system of NaBr and an oxidizer that works so as to keep an equilibrium of a very low concentration of Br2 at any time, like ppm or maybe even ppb concentrations, much as pool chemicals work to keep a low concentration of Cl2.
you definitly don't want to be in a closed room with an open container of Br2, nor do you want to handle it with out gloves and long sleaves, but irriitation to the mucus membranes starts to occur long before toxic levels are absorbed, and in terms of corrosiveness id say its less potent then strong acids or lye.
my point in mentioning that is not that one should be careless with it, but rather my point is that its not something terribly inappropraite for a chem supplier to offer to "amatuer" chemists, no more so then concentrated HCl for instance.