I am aware of the reasoning that URLs should not open in external apps for safety reasons. However, in Android at least, the OS itself gives you the option to define whether specific URLs will open in an external app or not. There's no reason for the browser to prevent the user from being able to open URLs in external apps at all when you can define it, within the operating system, on a per-app basis.
This issue is effectively the sole reason I decided to discontinue using Opera on my mobile and desktop devices.