Basically, it's a trinket that screws up enemy targeting a bit, sometimes making them retarget their attack into randomly chosen position next to wearer (in range of about 1-2 tiles). Only monsters that are attacking wearer using ranged weapons are affected, melee attacks are connecting as usual or affected less.
On pro side, it would make it slightly easier to deal with homing attacks (*ahem*RocketPuppies*ahem*), but on the other hand it would make regular attacks less predictable (anyone who has played Doom or Doom II remembers what happened when you picked up invis powerup ;) ).
As a possible additional downside, it could allow monsters notice you from further away.
In PvP, it could slightly mess up Autotargeting in the same way.