It's not a internal shifter because it does not shift from 1 gear to another as you well know it mearly changes the ratio by varying the contact points of the mating surfaces. I have 2 Nuvincis. Been running one of them regularly for over a year with more power to it than any of the builds I've seen on your bikes in the china girl division. Works great. I also have a 5 speed sturmey and a 4 speed shimano. They don't hold a candle to the Nuvinci, and no they don't need fiddling. Once you get used to it it's way smoother and easier to function than either of the latter two
I'll add that if I can drive my 220pound ass at 50mph through that exact hub then it must be good enough for most anyone. I have had more issue from my cables since I sometimes shift live and that means the shift mech is much more resistant to being moved, as a result I've broken my shift cable a couple times just from really cranking it under power.
The one cute part about this hub is it tends to shift towards its lower gearing if the resistance is low in the cable slide, under power it wants to drop. If you snap a cable you can hook the working length to the shift up nut and shift higher and hold the shifter to prevent it turning back. Letting it go and tickling the throttle let's it go back down.
It's twice as likely to break a cable, but the redundancy allows for some play that regular shifters don't have. Even without that accidental feature it's still much more robust than any other hub I've used, again due to just being able to use one solid gear and one very solid chain, every internal gear hub allows that, but those in themselves rely entirely on toothed gears inside to generate gearing, the nuvinci uses the novel approach of a transmission fluid like substance that is a non-newtonian fluid under the right pressure. That is the power transfer of the hub, no mechanical parts actually grinding or meshing, just the extremely durable sphere and 2 smooth races with the fluid in between acting as the "mesh" between parts.
The kicker is there is just nothing that can chip off or create debris inside the mechanics, internal geared hubs have parts that can quickly turn the rest of the system to dust once something let's go. The only part that's really at risk is the freewheel (one way) mech on the gear, and in videos and stories of failure that's the one part that really goes (other than cases of leaks on the earlier models of the nuvinci 360, said to be solved, mine does not leak.)
Definitely smooth, smoother than any transmission on anything I have ever ridden, you can't even hit it too hard, the liquid nature is a buffer so you can't drop the throttle, shift up and wring it with that horrible smack as the gears come to, just sweeps in and rolls nice. I really like that part because I can be a bit more aggressive on the gas without feeling like I'm going to break something.
