I believe the emergency services are using it. I am really surprised it is popular, mishearing one of the words, or getting them in the wrong order (which on all that I have tried is valid) takes you to a completely different location.
Then there are the homophones that W3W contains (Why? Seems obvious to me that linguists would have made sure there weren't any included, and treated all sounds-alike as being the same thing), some of them in close enough proximity to be believable but wrong enough to be useless.
W3W is a 3M square, there are 57 trillion squares on the globe and 40,000 English words used. Maybe 3M granularity is important, but increasing the size of that would have reduced the number of words which were needed. (By my maths a doubling the size of the square would halve the number of words required)
If my life depended on it I absolutely would not use them.