Due to their inclusion on the list, we clearly felt that each of those authors or teachers had something useful to contribute to humanity.

Nevertheless, we encourage you to use the same prudence when studying those teachers as you would with any other. Just as some examples, Dion Fortune (as far as I understand) was involved with black magic early on in her life, and Nietzsche went insane. Despite this, many works by those authors are highly beneficial to study. Samael Aun Weor himself recommended Dion Fortune's Mystical Qabbalah.

So study them, but do so wisely. Be awake while you're doing it. Investigate, use your intuition, and pray. And when in doubt, stick with very well established teachers: Jesus, Samael Aun Weor, Padmasambhava, Moses, etc.