get used to it - it will always chunk up. I have a small (3" dia) mortar and pestle devoted to just this chemical. I also ocassionally get a good sized pair of pliers down into my container of it to break up big chunks before I consign the smaller bits to grinding. Most of the time it is easier to make up a 10% solution of bromide in hot distilled water, and then just measure out the required mL to get the weight that a formula calls for. This means the pestle sees only seasonal use when the bromide bottle gets empty.
I deal with the BTZ the same stock solution way except I make it up as a 1% solution, since it is usually needed in such small amounts. Yes the material is certienly finely divided. One purchase of the stuff though, is usually a lifetime supply.