It is pretty worthless, so many people who i see activate it just live a little longer, you just sit their and wait for it to be done and finish them off. While using their shields dont regenerate, nor do they do damage to you (unless you hit them with a vehicle, but that is still annoying to time). The only hope of someone using that ability is that a teammate will save them in those few seconds, but that seems to rarely happen. There are many other abilities that are far more useful.