Not familiar with the book itself, but very familiar with John Clements. He's the director of ARMA, and very well respected for his knowledge and ability. He's also very controversial because ARMA is known to not really play well with other groups, so there's kind of an ARMA vs the rest of HEMA mentality at play, but I think even his detractors will agree that he's a very capable teacher and swordsman. You may just find that certain techniques in his book disagree with the rest of the HEMA community at large.
