Since I'm anyways living in Brussels and the fair is only a 20 min. trip by metro for me, I visited the fair yesterday. It was rather disappointing: only a handful of booths were worth looking at. The fair is infested with jewelry, specimens without name or label, copper sulphate crystals, "healing stones" and other assorted junk. The part of Pierre Rosseel's collection on display alone showed more specimens than all the other booths combined. In less than an hour I was standing outside again. And that includes the time to eat a slice of pie to support the organization.
In summary it's a good pastime when there is nothing else planned on a rainy Sunday afternoon for collectors living in the immediate surroundings of Brussels, but it's definitely not worth getting on a train for.