Re: Live tanto in grading
It has been said many times, but it's far easier to stab someone than it it is to protect yourself against an attacker with a knife.
I used to visit a local Tomiki dojo every week and found the shiai practice very interesting. The problem was that, coming from an Aikikai background, it took me a while to pick up the very specific rules about how to attack. I was paired off with a visiting dan grade from another Tomiki dojo, and immediately buried the rubber knife up to the hilt in his ample belly, to the great surprise of both of us! Since then it has become very clear that it can be ridiculously easy to reach someone's vitals with a knife, especially when the attack isn't restricted to the standard shomen/yokomen/tsuki directions.
I would definitely agree that using weapons with an edge is a great eye-opening occasional training aid. On the other hand, amidst the heightened stress - and eventually fatigue - levels of gradings its seems to me very risky to use live blades, particularly with unfamiliar ukes. I have seen so many airborne tanto and bokken as a result of over-enthusiastic blocks or careless handling.
I have fortunately never had to deal with a real-life knife attacker. I suspect that the results would not be nice and clean like they are in the dojo (whichever way the encounter went!).