How can we calculate the efficiency of the Siva Cycle Atom generator?
Taking 100kg of bike plus rider up a 0.3% grade generates a retarding force of 100kg*g*0.003=3N.  At 24 km/hr=20/3 m/s that is 20 watts.  If that is generating 1A at 5V, the efficiency is 25%.  

Yes, I picked numbers that were easy to calculate with.  But I believe this is all marketingspeak and you shouldn't trust the numbers to an order of magnitude.  

Note this claims the efficiency doubles if you slow to 12 kph. I suspect the efficiency is roughly constant and either the force decreases or the current available increases as you speed up