Probably the most luxurious gear hub you can find. 14 evenly-spaced gears, range of 526 %, everything runs on ball/roller/needle bearings, the internals are lubricated by oil bath and sealed from the elements. Service life is in the range of hundreds of thousands of kilometres, maintenance is zero except the yearly oil change. Price equals that of a complete bike of good quality and equipment.
There are many versions and their parametres can be selected in almost any combination. Axle is either solid, hollow for a quick release skewer, or emulates a large through-axle. There are 32 or 36 spoke holes. Shifting mechanism is either internal (two rubber-coated "worms" stick out from the hub), or external (see photo) which can be combined with brake disk (with a proprietary four-hole pattern). Torque reaction arm is either long which anchors to the frame, shorter which anchors to disk brake mount, or shortest which needs special dropouts (see photo). Then there is an ultra wide version for fatbikes, ultra strong for tandems and maybe more. Sprockets come with 13 to 21 teeth (except 20), 16 is standard, and only in 3/32" thickness - a pity, 1/8" would certainly be more durable. The sprocket sits on a splined driver and once you wear it out, you can turn it around and use the other side of its teeth. Twist shifter comes in right or left variant, no other options (like triggers or bar ends) are available. Hub flanges can be further reinforced by aluminium rings (I don't know why they don't just beef up the flanges by default).
Other things you find in the hub's box are twist shifter, cables (with rubber-sealed end caps), a bottle of oil for the initial fill (the hub is assembled dry) with a filling tube, spacers which let you remove the no longer needed extra chainrings, a decorative sticker, some papers and a detailed 150-page manual (PDF copy is freely downloadable). And any extras like brake disk or chain tensioner which must be ordered separately.
To be honest, I don't know. There are two or three epicyclic stages inside with cogs of many different sizes, and considering the number of gears, each of them must be used in several different modes. Gear 11 is direct drive, 1..10 are underdrives and 12..14 overdrives. There are two shifting cables instead of the usual one, so no return spring is needed. Indexing ("clicking") occurs inside the hub, so the cables and shifter need no adjustment. The clicking is amplified by the springy spiral cable sheaths, but they are too short on my trike to show any springiness, so the shifting is very light and sometimes I'm not sure how many gears I actually shifted. But it is no problem since you can't hit an intermediate position and with the small steps between gears it feels like a continuously variable transmission anyway. According to the manufacturer, shifting under full load doesn't damage the hub, it is just not guaranteed to reach the gear you were aiming for (I can confirm that, easing off is necessary). It takes about 1000 km before the hub is properly run in and noises and resistance drop to their nominal levels (that's harder to confirm because the changes are too slow to be perceptible).
For the external shifting mech, I'd recommend leaving the cable ends a few (3..5) millimetres longer than the 200 mm recommended by the manual. It causes no problems (easy to compensate by the adjusting screws) and makes it easier to wind the cables around the pulley. Caution: cable ends get frayed by the pinch screws in the pulley and if you take them out, you never get them back in. Before tightening the screws, be smarter than me and make sure to check twice that all the necessary parts (cable sheaths with end caps and both adjusting screws) are threaded on the cables properly.
Once a year (due to moisture which got inside the hub) or after every 5000 km (due to accumulated particulates), oil needs to be changed. Compared to greasing, it is a trivial operation: unscrew the plug, screw the hose in, squirt in a dose of thin cleaning oil, spin all the gears thoroughly, then drain everything and replace it with new lubricating oil. Of course, these are proprietary and accordingly expensive oils, so it is better to buy them by 250 ml bottles which will keep you going for ten years. It is not a good idea to use WD-40 for cleaning and some cheap transmission oil for lubrication because they might eat the rubber and plastic parts inside.
Caution: the hub is not sealed perfectly (it can't be), changes in temperature and atmospheric pressure keep squeezing tiny amounts of oil out of it. Normally this is not a problem, much more oil sprays from the chain, but if you have built some monster bike like me and your disk brake caliper is below the wheel's axle, you must regularly wipe the area around the left seal. I didn't and after a year of uncontrolled accumulation of greasy dirt, my brake pads soaked up so much oil that they stopped braking.
After first three thousand kilometres there's nothing to complain about. We'll see after first few years.