Now, I don't know if, say, Wolters Kluver would/does the same thing, and what the realistic risk of an individual receiving such a letter is, but I think it makes it worthwhile to go over the actual law in your jurisdiction before diving head first on things like this.
I'm not saying it's wrong to seed these things, I'm just saying it might be a good idea to weigh the risks if you don't have a cool 500€ in cash to part ways with.