So far I have tested a couple of good quality red 3 pliers pliers and they all pierce the plastic and when heated the piercing opens further exposing the metal. I'm a marine electrician and I've done 1000 crimps. If there are no super crimpers, it becomes difficult to get a waterproof connection that also passes the pull test. Update** I bought their custom crimping tool and they don't pierce the insulation like a standard crimping tool.