I don't use Nu-Opera, but when I used classic Opera the main selling point for me was not needing extensions. I have neither the time nor the expertise to curate extensions and stay up to date with new browser trends. Built-in features mean that I'm only trusting one entity rather than entrusting my privacy to a half-dozen individuals or small teams, it means that there is a stronger guarantee of maintenance and not breaking, there is a stronger guarantee of inter-op, and when something breaks I have one place to complain to rather than wondering if it's an obscure interaction between three pieces of quasi-independent software. The overall experience was much more seamless than what it would take to collect the equivalent set of feature into Firefox.

... the "trusting one entity" was a big part of the sell for me originally, and it a big part of the reason not to use Opera anymore. The company was purchase by a Chinese investment firm, which I'm a little light on details but seem to recall them being heavily invested in advertising.