Despite the fact that Apple doesn't want apps that "duplicate" the functionality of native Apple apps, I think having multiple apps for the same chores is one of the strong points of the Mac and Windows platforms - and should also be for iPhone OS. As long as the Apple apps are the default on a new phone, most people will use them at first and decide if they like them, or if they want to go off and fetch another - like Opera here - and try it out.
One example I can think of is shopping the App Store on the iPhone: I really prefer AppSniper to Apple's Store app. It makes shopping better IMO.
I think sales of physical units surely must be the most important factor here for Apple's bottom line, so I am really happy they approved Opera, because it makes the platform all the more user friendly.
In the case of Opera vs Safari, however, I still prefer Safari.