Also it looks like you can't shift under load with the internal hubs which is a problem if you are trying to climb hills quickly.
Maybe in the more popular implementations like from Shimano. But there's internal hubs with greater ratio spread than chained: The Rohloff:
Here's a discussion on the subject of shifting under load, with opinions from "both" sides:
In terms of friction, there are no jockey wheels and the chainline can be perfectly straight. Anyway, the internal friction of a geared hub is going to be unnoticeable for an average cyclist because the tires will be under-inflated, the chain covered in crud, and the brakes will be rubbing on untrue wheels.
But like everything it's a tradeoff.
Geared hubs are great for riding in traffic because you can shift while stopped. Pulling harder with traffic up to a light and braking aggressively, and switching to the right gear while waiting for the light to change.
Like everything it's a tradeoff. For me, geared hubs make a bicycle a more useful tool. Less fragile. Less maintenance. Idiot friendly static adjustment.
The Nexus eight speed is the seven speed with a “granny” gear. The seven high gears have small steps relative to a five or three speed. I suspect this might make shifting under load less stressful on the components...note that under load shifts are always just one gear at a time unlike a derailer.
The Nexus 8 is a great piece of kit. Robust, inexpensive and stupid easy to tune.
It is less efficient (apparently). But at least it's consistent. Ride a chain in the rain for just a couple days and trust me, it's nowhere near that theoretical 95%.
The efficiency (like all other marginal gains in cycling) is important for racers or long-distance tourers. For everyone else it needs to be considered against the maintenance burden required to maintain an exposed drivetrain which needs to be cleaned, lubricated and adjusted in order to maintain its relative efficiency.
And weight...