The company's claim only works if going faster and being more efficient are the same thing, and the strongest way to break a weaken question is to show they are not the same thing here. If using the software also means making a lot more mistakes that then have to be corrected, the "30% faster" number stops meaning anything about real productivity, because the time saved gets eaten up by the rework. That is exactly what the independent-audit option describes, so it lands hardest on the claim. Statements about employees liking the software, the software costing less, a handful of employees finishing even quicker, or a competitor's tool never say anything about whether the finished work is actually better or worse, so none of them touches the company's real weak point the way the rework-from-errors option does.