Some more info:
I was talking to him after the crash and inspecting his bike and noticed that he had the cord attached to the tail section of the bike, up by the seat. I told him that the recommended mounting location is up by the forks, and that the cord should not have excess slack while riding.
One serious disadvantage of the tether system is that it won't deploy if you are close to the bike, as is common in many lowsides. However, many injuries can and do happen after the initial impact, and many crashes involve immediate ejection from the bike, where this system would work instantly.
In any case, it's another safety option. It is not perfect by any means. I will say that it is not intrusive while riding in any way.
One last complaint is that it doesn't look very cool, but I haven't looked cool in years. When my bike rolls through tech, people look away!