Antony Cummins is a guy who co-edited a translation of an old Kishu ryu/Natori ryu ninjutsu scroll. For this reason, before the book came out, people needed to post photographs of his parents' house on the Internet:
Antony Cummin's new agenda - Page 3 - Martial Arts Planet
After spending some time practicing xkan-style martial arts and investigating some of the very limited primary source material on ninjutsu in the past that was available before he began his research career, Antony reasoned that xkan martial arts isn't ninjutsu and ninjutsu wasn't combatives. Westerners who practice martial arts have this odd habit of tying up their martial arts practice with their whole sense of self, so needless to say, this rustled some jimmies. On the Internet.
He decided to make it his career to find a way to get the well-known and obscure primary source texts for ninjutsu translated and published. He does this commercially, not academically. This doesn't necessarily mean he does it wrong.
Antony isn't liked by the xkan officialdom on the web because they perceive that to undertake such a project requires in some way their authorisation and he acted without it. He used all of the heat like you can see in the link above, to drive traffic to his YouTube channel and in this way built up his brand from scratch and in fact created his own constituency for his books before any were published. Publishers love this. It was a brilliant (and often hilarious) social media campaign.
Japan has always been a highly literate culture but never had anything like centralised institutional record-keeping, universities, libraries or cataloging as in Europe. As anyone doing research in Japanese history knows, source identification can be a pain in the face; everything is local and usually privately owned. Antony regularly maxes out his stay visas in Japan traveling to local libraries and archives, specialist antique book dealers etc. He goes to libraries and goes through literally every old document they have, logging every occurrence of the kanji 忍 for later investigation. By contrast, the content of those who have taken it upon themselves to self-identify as critics of Antony, consists entirely of kvetching.
One thing that really hurt the feelings of people on the Internet was that Antony reached out to ninjutsu reenactors on YouTube for collaboration. These reenactors usually claim to be trained in one sort of authentic ninjutsu art or another and this of course causes apoplexy. Those that got over themselves were able to see that Antony was making a clever point in a smart-Alecy way: there is NO authentic tradition of ninjutsu around today - the YouTube reenactors, and the xkans are equally not ninjutsu. Imagine the salt.
Remember, Antony spends his time in obscure archives looking for and finding obscure texts. Then he has them translated. Publishers are kicking his door in to get this content. Anyone taking to the Internet to critique him who hasn't done at least similar, can be safely ignored.