For a minute think you are the customer. Would you choose to answer with a number or some text. Well, if the survey is long it will be definitely be numbers. Unless you are either awed / very dissatisfied with the product/service. Using NPS your data could easily tell what product feature/service/area of your support is working for you and what's not.  But I would suugest if your are going only for NPS you won't have the whole picture. Some text based feeback is also required which you can further convert into NPS based on the Keyword or tone of the answer. It will require manual work though. But you can outsource it.

Great points @dharmu89. Also, I believe the answer to this question is in the more in depth aspects of what you do with the NPS score once you have it. Would love to get into the details of the "metricize" part. This is a great article within this one that breaks down understanding the "why" behind the data - http://blog.wootric.com/understand-the-why-behind-your-score-real-time-nps-by-customer-segment/. Thanks for sharing @lisaabbott!