My analysis of this app demonstrated that while the three word algorithm described locations with commendable accuracy, there was zero redundancy in the system. If one of the words is misspelt, misheard, or transposed, you either end up without a match, or at a random location often many miles from the intended target.
By comparison a latitude and longitude location should be universally understood and although the absence of one or two digits will reduce accuracy it still allows an approximate location to be inferred or determined by a bit of logic and analysis depending on the circumstances. Nothing more than a pencil and a scrap of paper required to work out possible alternatives together with a basic understanding of maps and navigation.
I would venture to suggest that any moves towards using proprietory location systems rather than Lat/Long coordinates is ultimately divisive and potentially dangerous. Such proprietory systems have their place in commerce for specific functions, e.g. postcode and zip code locators, but their use needs to be restricted to their intended purpose.
Why reinvent the wheel when there is already a universally accepted standard that has worked for centuries which also forms a perfect match with the physical world and time keeping? On the surface, a great idea but ultimately deeply flawed in execution.
Finally it must be stated that if the sole purpose of What Three Words was to describe a location anywhere on the World’s surface using a single unified list of words for all users, it might be considered fit for purpose. All the above mentioned drawbacks arise when the software is put to uses other than those originally intended. Find out how to display Latitude and Longitude on your phone or other devices. Those coordinates will ultimately be of most use for navigation or calling for assistance when needed. They also describe any location on Earth with absolute precision.