I've heard that.

I had a store of those once, but I kept hearing how toxic they were, and they went far past their expiration dates, so I got rid of almost all of them without using them. I've also heard the the ash/residue is toxic.

Though behaving similarly, Esbit tablets at least claim to be non-toxic, unless actually consumed. I know that generations of kids have used them to power their working-model steam engines, and I don't recall anyone even considering moving them outdoors before firing them up.