It is quite old thread here, but nevertheless the topic is still on spot. I actually found this thing out by surprise, when spotted sitecheck2.opera.com on wireshark capture "flood" while troubleshooting my home network.
It has been a (popular) habit to accuse Google of "spying" on us with their browser, but now we have here something built on same code base, but even more locked up - without ANY options to switch features like this off.
It might be "bought" by big public, that this is done for a sake of our safety and security, but this kind of total lockdown (which even Google itself does not implement) can only be perceived as a guarantee for solid source of data, which is quite probably used for some business purpose. If Google collects my browsing data, it can provide me with better search results and "get smarter" for my use, but it's hard to see, what additional value can be for me in return for this "data mining".
Things being this way there might be only one valid solution - to stop being this "data source" and ditch the browser. Have been Opera user for 15 years and seen many things to happen, but this one "takes the cake"...