NPS has the advantage of being concrete and simple, producing evenly sampled feedback. This is hard to get any other way.
A proper NPS asks only one question and requires only a single click to answer -- eg "Scale of 1-10 how likely are you to recommend to a friend?" > click [8] > done.
There's a free-text "Tell us more" field that is totally optional.
This means users actually answer it. NPS feedback is the closest I've ever seen to being a clean sample.
By contrast:
- Everyone hates an n-question "would you like to fill out our survey" feedback form. Any data from those is going to be skewed, because only a certain kind of person fills those, and usually only if they're angry enough that they want to vent.
- Feedback from a passive "Submit feedback" button in-app is also skewed. Maybe useful as a bug report mechanism, but it won't tell you what's making your happy users happy.
- Proactively reaching out and talking to/observing users is obviously good, and nothing ever substitutes for that. But you want bulk data, not just anecdotal evidence.
- Most importantly, NPS really shines at telling you what's making your almost-happy users almost-happy. When someone clicks [10] and writes "I love it", that feels great. But when someone clicks [7] and tells you what's annoying them, that's often extremely useful.
- NPS does a great job priming people to give useful feedback. By forcing you to pick a single out-of-10, you just did a quick mental accounting. "9? Nahh, ." Then you click 8 and write the reason.
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NPS was popularized by that famous HBS study where they found it correlates well with product growth.
I wonder how much of that result is simply because it's one of the least obnoxious ways of sampling user feedback, and therefore produces clean data.