If you notice, it is a very coarse salt that could not by eaten on food unground (OK for cooking as it will dissolve).
It is intended to be used in a salt mill. I have a combined salt and pepper grinder. I'm not sure why someone would tell you that very coarse salt shouldn't be used in a salt mill, as that is exactly what this is intended for. Salt mills, or grinders, have ceramic grinders because the corrosive qualities of salt would destroy a metal burr very quickly.
This is the grinder (or mill) that I use.
(Not my photo...and without the pink salt!)
Image
BTW: I was told that this is a very "dry" salt...and my experience is that it never clumps up in the grinder.