Okay, hadn't seen Antony before (kinda wish it was Alan Cummings, one of my favourite actors....), but we'll deal with him in a second. First to "Choson Ninja", Greg Park.
Um, not sure if you are aware, but on MT there are very strict fraudbusting rules, so I'm going to be as careful as I can in what I say here....
Greg claims many things, including a Korean version of Ninjutsu (a translation of the Choson Ninja name is "Korean Ninja"), and also claims a very Christian-based spiritual approach to why he is teaching (the name Choson Ninja is also said to have been chosen for it's similarity to "(The) Chosen Ninja"). He has had a long string of YouTube "lessons", with no actual dojo (and by extension no actual students), and he always comes across as being humble, dedicated, and sincere in his approach... except that there is nothing backing up anything he says, or claims, at all. His take on history is incredibly suspect, to say the least, and he has (a few times now at least...) gone out of his way to say he is not claiming to be teaching ninjutsu or anything related, as he respects the Bujinkan and related organisations.... and then continues doing what he said he wasn't going to. So, essentially, I see many people defending him because of the way he presents himself (humble, sincere, honest etc....), despite there being no backing to his inconsistant claims. Not someone I would pay attention to, although he certainly has fans (occasionally Bujinkan members, according to the comments.... although I'm not convinced of that either, my cynical side feels that they are plants to further his credibility).
Now to Antony Cummings....
I went through a lot of his stuff, and while very interesting for the most part, a number of things just didn't add up for me. To begin with, the study of combative methodologies throughout history, specifically from a more anthropological point of view, is known as hoplology, brought into popularity by the late Donn F Draeger. Within this field there are arguments as to which is the better method for understanding, an emic (included) approach, where you are part of the thing that you are studying, essentially an insider's point of view, or an etic (excluded) approach, where you are removed from that which you are studying, an outsider's point of view. It has long been held by hoplology students that the emic approach is the prefered method in this regard.
When it comes to Cummings, his approach has been entirely etic, rather than emic, and in fact, is taking only a single account of that which he is supposed to be studying. He constantly refers to historical accounts such as the Shoninki, the Bansenshukai, the Ninpiden, and others, and relies on a man he claims is the foremost expert on ninjutsu and ninja in Japan, a man who all international television shows come to for information, someone he simply refers to as Nakashima Sensei. He doesn't reveal exactly who Nakashima Sensei is.
However, his website does have one or two photos, and I have a few books with me. I thought he looked rather familiar, so I double checked. The gentleman in question appears to be Nakashima Atsumi, best known to the West as a teacher of Serge Mol, an author who has written a number of books. These books are very good overviews, however there are a number of innaccuracies throughout them, and Serge has been known to have a rather thinly veiled hostility or prejudice against the Takamatsuden schools. Nakashima claims the title of Soke to the Katayama Hoki Ryu, which is a reconstructed school.
Cummings claims that Nakashima is the greatest ninjutsu historian in Japan. Well, that really is a matter of opinion. And I'm not sure I would class him as that. The next point is a little odd, or at least seems that way... Essentially, it comes down to the emic versus etic aspect of study. Antony has been exclusively etic in his approach, looking to old incomplete documents for his information. He has then drawn incomplete conclusions as a result. For example, he claims that there is/was no actual martial system of ninjutsu (although he seems to contradict that when he talks about certain groups engaging on battlefields, and constantly describing ninja as part of a warrior culture), as the documents he has seen have no techniques listed or mentioned. The thing he misses there is that they are not technical documents, and are not to be taken as technical manuals.
His claim is that there is no documentation he can find of ninjutsu techniques in documents such as the Bansenshukai, which is fair enough. What he sees is a lot of reference to espionage, spying, and so on, so he draws the conclusion that that means that there was no physical martial art that was called ninjutsu. In fact, if anyone claims to be teaching it as a physical art, they are by his definition fraudulent. I would counter that by (gently) pointing out that he has no emic understanding of the various ninjutsu-related systems teachings... The Bujinkan, for example, is made up of 9 systems, only three of which are classed as ninjutsu. Two of those (Kumogakure Ryu and Gyokushin Ryu) have not been taught publicly, and it is thought that they may not have formal techniques, although that is not the same as having no martial art. The third, the Togakure Ryu, certainly has physical techniques in it's teachings, although they are rather different to many other arts. The basic philosophy of the Togakure Ryu is more in the avoidance of violence, but the techniques are there.
This is obviously only one instance, but frankly I saw quite a lot of things in his presentations I would at the least query, if not downright argue with. Add to that some bad pronunciations (ninjitsu from time to time, reference to ninjas [to pluralise], and what seemed to be a complete misunderstanding of what the term jujutsu actually entails from a historical perspective, or how it should be applied) has left me a little unimpressed. He can give you a few things to think about, but he's not really a reference I would go to. He's just far too limited in his own understanding and knowledge, frankly.
). If on the other hand you run a dojo and hope to make a living out of it, for which you would need enough students. Well, in that case you're probably boned. 
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