Alexander doesn't explain his opinion, so I may be missing something, but I think he is wrong. Sure, you probably won't fool magicians with this material because as Dan himself points out, nearly all this stuff is 100 years old. Plus, lots of people already own the books. But I think if you do already own the books, these downloads will be even more valuable because you will then have two often very different presentations of the same trick, which should inspire you to broaden your horizons and hopefully come up with a third presentation that is best for your own style.
Also, Dan has improved the methods in many cases. His way to make a gimmicked screw-top jar is totally new to me, and I own a lot of magic books.