This video shows how the SA kickback hub operates. The two speeds are direct drive like a one speed, and the second gear is 138% higher. You switch between gears using your pedals. A slight rearward motion will shift the gears.
On this hub, it has a coaster brake. So pedaling all the way back is your brakes. They make a freewheel version also. There's a downside. when you pedal back for brakes, you shift gears also. So if you were in low and hit the brakes, you would now be in high gear. From a stop, you would have to start out, then shift back to low gear. The hub must be turning to shift. An advantage is no shift cable or shifter to adjust.
If you ride this one hub all the time, shifting becomes second nature, and is easy to coordinate.
On this hub, it has a coaster brake. So pedaling all the way back is your brakes. They make a freewheel version also. There's a downside. when you pedal back for brakes, you shift gears also. So if you were in low and hit the brakes, you would now be in high gear. From a stop, you would have to start out, then shift back to low gear. The hub must be turning to shift. An advantage is no shift cable or shifter to adjust.
If you ride this one hub all the time, shifting becomes second nature, and is easy to coordinate.