I was using one called YouTube Downloader, by flaviobayer, but out of curiosity I have now tried the one you are using and it seems pretty much the same, with a Download button where you can choose format and resolution for downloading. There are lots of them - just go to the Get Extensions page in Opera and search for YouTube and loads of them come up. I've tried a few and yours is as good as any. There's another one I've used called ExtendTube that gives you other facilities as well as a download button.