Even though it inflicts no damage, the clan version can make it so an opposing mech has to choose: do no damage to you (not to fire any weapons) or to risk ammo explosions, shutdowns etc. The IS version is great because it compares pretty well to a PPC or AC10 with 10 points of damage AND heat. Most hits will affect his movement, and accuracy, and if he is already riding up the heat curve you could push him right over the edge.
Even better, against players who completely avoid ever putting some heat on at all, could find themselves in very uncomfortable territory. I know a few players who would freak if they ever found themselves in double digits on the heat scale.
I wouldn't go for it as my only weapon, or even my main weapon, but being able to throw a wrench in someone's perfectly balanced heat management [tickedoff](or finely tuned turn of TSM perfection): priceless.
