Text: When you are destroyed, each ship at range 1 takes 1 damage.
http://www.fantasyflightgames.com/ffg_content/x-wing/news/scum-and-villainy/dead-mans-switch.png
Put this on something with a low PS, get it in the middle of the enemy, and then fire Assault Missiles at someone near it. Hit them for one, then trigger the Switch to hit everyone again.
You are assuming the enemy won't just move away from that low PS ship you are using and you are assuming that it will be on only one health. Too many unlikely assumptions, something that seems to be fairly common it seems unfortunately when people are assessing the new S&V stuff.
And this is a shame because decent uses for these items are fairly obvious when viewed for use in moderation. The Dead Man's Swarm is a good example of how it should be used.
All of list building is predicated on assumptions.