This seems quite a powerful combination.
You gain a +2 item bonus to all defenses against attacks from enemies that are subject to effects caused by you.
Enemies within 10 squares of you take a –2 penalty to Insight checks. Those enemies are not aware of this effect.
So the real question here is if a -2 penalty to Insight is an effect caused by me?
For an even better combination use Skull Mask. It is not only cheaper, but the properties are actually useful.