34.3% chance per second with 4 shaman to knock someone down. not sure how long the knockdown lasts or if it has a cooldown, but its also a 4k per second aoe.

All in all, doesnt seem good for single target when you can insta-gib instead, but if youre standing back and can free cast it on a lot of enemies while they spar with your team-mates, you should be able to turn the tides pretty well