Dont think you can change storage folder for Opera for Android(without logging on as root), because of this i think is just a waste space on a Android device. I have used Opera as my main browser for 15 years, I will most likely end my Opera use as i think this should be easy "fix" but Opera jut dont bother. I am quite mad and I have been known for fight lost causes, I also boycott websites that use Adobe Flash because Adobe make Flashplayer for Android.
I do hope that people follow my lead, then things may change.