It takes out 10 cm armor at 100 meters, according to article. I wouldn't call that inefficient.

What I see is weapon designed by a State for use by terrorists or insurgents. It's a pretty primitive and inefficent weapon for the application of a conventional war. But as specialize weapon for terrorist it's nearly perfect- it's probably as significant as a stinger missile.
The downside to it [for the Iranians] is it's got Iran's name all over it- therefore shredding any claim to deniablity. Iran is at war with Iraq and Coalition forces. How long are we going to pretend they are not?

And I imagine this might be the tip of iceberg.
Think of it, the terrorists "suffer" from weapons not really designed for their purposes. What happens if a State is focusing billions of dollars in research and development exclusively for weapon systems to be used by terrorists?

We got the suicide belt/vest [low tech] and we got this shape charged mine [much higher tech].
What else have they developed and are developing?