I am thinking it is another one of those things like firearms.
Police (at least in California) are so worried about issuing concealed weapons permits and pretty much wont issue them to anyone that apply for them.
All that does is prevent legal law abiding citizens from carying, I for the most part wont carry because I have too much to lose if I get caught.
But a criminal doesnt care, they will carry because to them it is worth the risk
This stupid bracelett, I am thinking all law abiding citizens would wear it, but if I were a terrorist I am thinking all I would have to do is place some kind of rubber sleave in between the bracelett and my wrist. I bet there would be an easy way to bypass the bracelett, so in the end everyone has a false sense of security, the government shells out large amounts of money for a flawed system.
And this doesnt even take into consideration the possability that a terrorist could learn how to activate these devices and maybe activate them and disable all passengers.
What if terrorists were able to take over a plane and gain control of the system? they could then affectivley control the passengers. If a group of passengers tried to take back the plane the terrorists could imobilize the passengers. It would basically assist the terrorists in controling a plane.
bad idea in my opinion
As a matter of fact if I see anything more on this where it seems they are pursuing I will probably end up contacting DHS about it, that is how bad of an idea I think this is.