What3Words had a lot of potential, but they hurt themselves by aggressively going after alternative/open versions with legal threats instead of encouraging an open ecosystem. Also, the system can make serious mistakes — similar-sounding addresses can easily point to completely wrong locations, even nearby, which is dangerous in emergencies.
I agree it would be great if smartphones had a QR code scanner built-in. It would save lots of code duplication for basic tasks.
On the other hand, you would have to trust that native app being the 'man in the middle' for the data scanned.