Hi Gareth,
Nice to hear from you. I really enjoyed Geoff's seminar.
As you say it is not "authentic" medieval unarmed combat, but is rather adapted from it. It is improved even. His knife disarms are much safer (you get the hell out of the way of the sharp thing) as are his blunt instruments methods.
OK, I believe there are a couple of misconceptions here. First, modern military CQB in the Fairbairn/Applegate tradition is adapted primarily from Jujutsu. This is not to say that there aren't similarities between Koryu Jujutsu and Medieval martial arts but the truth is the truth. There is no evidence whatsoever that the primary influence on the FAS system is western in origin and every chance that it is based on Judo/Jujutsu atemi.
As for the knife work being improved, I strongly and wholeheartedly disagree. Folks, Geoff teaches you to half inquatarta away from a blow and strike to the knife arm. This is completely different to the Applegate method some of which looks like it could have come straight out of Talhoffer.
The medieval defences do not generally have you moving to a position that keeps you inside of the knife unless the opponent is delivering a backhand. The key to the medieval, the Japanese and even the Filipino counter knife I have studied is to get to the outside line of the blow. If you get to the outside line of the blow then the attacker is forced to reorient himself dramatically to continue the attack. This buys you time to try and restrain the knife or counterattack. If you move inside the arc of the weapon, the attacker can not only keep pumping the knife at you but he can also shield it with his off hand. I believe that inside the arc of a knife attack is a bad place to be.
As for the axe kick working against a plate armoured opponent, I would have to say that the armour would likely provide a fair bit of deflective protection. Shane? Matt?
The axe hand to the neck/head area would actually cause quite a bit of jarring. Having been hit by this type of blow in the head (and once accidentally in the neck) in a reasonably authentic helmet and felt the effects, they would have to be worse if you were being hit by someone wearing a maille or plate gauntlet.
Cheers,
Stu.