I think knives are a pretty terrible self-defense tool IF your main purpose is to incapacitate your attacker(s). The actual loss of consciousness or DEATH usually comes from bleeding out, and unless you hit a major artery (and even if you do), it can take several minutes or longer - an eternity in those kind of circumstances. Strong impacts to the head or neck that cause the brain to shut down work far better (or catastrophic damage such as a shotgun blast to the body/head). Biomechanical cutting is still unproven. Of course, a combination of the above would work better, and Janich might very well advocate such use but having never trained with him I cannot say.
I have yet to buy the Yo2, but it's on my list and I think either would cut and stab well enough if pressed into the self-defense role. Just don't count on it working as fast as you might hope. re: lock - I have almost as much confidence in the Compression Lock as I do in Cold Steel's Triad lock. I just don't see it unlocking unless several fairly strong steel parts experience catastrophic failure.
Re: Force to the tip, essentially humans naturally use arcing motions whether it is in punching, kicking, or in this case, cutting. So, from what I understand, the concept was to have the wharncliffe blade so that as you are slashing, the edge is at an angle such that force actually INCREASES as the blade arcs through the limb or body part in question, thus increasing the depth of the cut especially as the tip passes through and presumably increasing the damage to the limb and thus potentially disabling it by slicing through muscle/nerve/connective tissue. My quick tests on various media with a couple of wharncliffe blades replicating tests by Janich and many others have seem to prove this. This especially seems to hold true for soft media such as raw meat - while it is not a perfect test, generally wharncliffe blades will cut much deeper than the blade length with any quick slashing motion.