Outside of the mount/dismount issue, what are you talking about?
What do you mean by "Height adjustments"?
What do you mean by "Emergency Stop"?
Efficiency?
Ok, I'll grant that a kid would need a smaller frame than an adult and a 6'tall + adult a larger frame than an average adult. Bicycles do come in various frame sizes, why wouldn't this.
I'm puzzled about the emergency stop argument because if you even looked at the images you'd see this thing has not one, but TWO disk brakes--front and rear. Your feet are for GO, not stop.
And the overall efficiency would be incredible because your feet aren't carrying your (average) 200 pounds, so all that walking musculature can go for acceleration, not load bearing. You could "walk" 50 miles in a day with one of these and hardly feel it. Get tired? Coast a bit.
I believe it's far more practical than you think.
