Not to mention he also created "The Lone Gunman" which is specifically cited in 9/11 CT circles. As his interviews show, he has clearly looked into the 9/11 CTs. And as JAStewart points out, he spent many years working closely with the CT mindset.
So yes, he has a LOT to offer.
-Gumboot
Do you think he has as much to offer as, say, Craig Bartmer, a former NYPD officer who was at the scene?
Bartmer was at Avery's house when they interviewed Avery. Bartmer asked to be interviewed and they refused.