This doesn't stop the cookies from coming through. If you enable dialog blocking, Opera will allow sites to set cookies as a matter of course. That won't be an issue for many people, but it's worth noting if you want to block cookies on some sites. It's not certain how the European Union will react to Opera's move, but it's safe to presume that you're consenting to cookies by enabling the option.
You'll have more to try in the new Opera release as it is. You now have home screen shortcuts if you're using Android 7.1 or later, and there's now a universal text size slider on top of the existing text wrap feature. Whatever you're looking for, Opera is once again betting that conveniences like this will draw you away from heavyweights like Chrome.