Denmark, where I live, is the land of coaster-brakes.

Just my 6,95 Euro:

Single-speed coaster-brakes are excellent. They are sturdy and reliable, and the brake engages in all weather. And you can brake with both hands off the bar. (You'll learn in no time.) Excellent if you want to transport another bike beside your own.

Multiple-speed coaster-brakes are another matter. They are reliable too. Sturdy, they are not. If you plan to give the bike any punishment beyond the sunday ride to church, you'll run into trouble. The delicate mechanism simply cannot stand the strain of even a moderate amatuer. You'll experience gears that doesn't function perfectly, needs to be readjusted often, and finally the hub simply cease to function. Furthermore, energy is wasted in the transmission. 20 years ago, 10% was a rough guideline, but I would believe it is less now, especially on a new hub.

With a single-speed (and probably with a multiple-speed too) you have to pay attention to something called "Konus" (At least thats what it's called in danish.) It is adjusted on the side of the hub, I don't know excactly how. But if it is to tight, it creates friction, if it is to loose, the brake doesn't brake as well as it should.

There might be some "super-hub" I haven't heard of, but Shimano-Nexus is not it.

The graveyards are littered with bikes thrown out, mainly because the internal-hub-gear has broken.

Edit/add-on:

Single-speed coaster-brakes are low-maintenance, probably as low as normal SS.

Multiple-speed coaster-brakes are in principle low-maintenance too, but the "sum of all bothers" is higher than with derailleurs.