Here's the hard evidence. It turns out that it actually is not the best measure for customer satisfaction. However, to me, it seems as long as you pick a reasonable method for measuring your customer satisfaction, that's fine. NPS is fine. Just don't expect that NPS is the end of the world. There are actually other metrics that are somewhat better. But as long as you use something that gives you that feedback loop about how your customers are judging your performance, both products and service. That's what counts.