Testing bike provided by Michal. Thanks!
Eight-speed gear hub intended primarily for city bikes. It has a range of 307 %, gears 1..4 are underdrives, 5 is direct and 6..8 are overdrives, so you don't have to change your chainring when upgrading from a classic singlespeed hub. If I'm not mistaken, sprockets of 16 to 23 teeth are available. Brake options are either none or a backpedal brake.
Shifting grip turns in an opposite direction than usual: backward for faster gears, forward for slower. In case of cable failure the hub defaults to gear 1, so you would be able to limp home - slow, but steady. The cable winds around a pulley hidden behind right dropout, similar to the S-A X-RK8 reviewed earlier. Unlike it, the shifting is smoother, needs less force and the difference between directions is minimal. Many other differences are hidden inside; Shimano has to use its epicyclics in both directions, not just in overdrive mode (that's the only way to get a ratio very close to direct drive). I don't know how it exactly works, the only thing I figured out during a short test ride was that backpedaling doesn't work as a universal reset here - the backward motion is somehow blocked between certain gears, so just stop or slow down pedaling when shifting. Efficiencies are hard to judge, 20" folder and 26" citybike are incomparable. Shimano says "efficiency: high", I say "I haven't noticed any significant drag during the few minutes of riding".
I don't know anything about durability or maintenance. The owner has been using his hub for about a year and hasn't taken it apart yet because it works flawlessly. If you have any experience of your own, feel free to share.