Correct if you're luck the proc rate is slighty higher then a lightning strike so the efficiency of them is going to really depend on what you're fighting, your build, and the group.
If you've got a caster in your group that's running around with a dreamspitter neg leveling everything that's stunned or held that vacuum II's will absolutely destroy everything. That's why if you're really interested in testing them out I would stick them on a Rogue with the Assassin ToD set with an Enveration guard as well. You're constantly deleveling things making every proc of the TTS kill regardless of content.