How can we calculate the efficiency of the Siva Cycle Atom generator? The Atom is a bike electricity generator made by Siva cycle and launched via kickstarter.

I was curious about how this generator compares to others (eg. hub dynamo/generators) in the market in terms of efficiency. 

Quoting from the siva cycle FAQ:


  How much resistance does the Atom add to riding?
  
  The resistance is very small, and is proportional to how large your charging load is. At full generating capacity, it is akin to riding with your tires at 70 psi instead of 90 psi, or pedaling up a 0.3% grade. In our use around town, it is very difficult to tell that it’s on the bike.


I think the full load on the generator implies drawing 1A of current through the USB port at 5V so thats 5W of output assuming perfect voltage conversion. 

Is it possible to calculate the efficiency of this generator using the above information?
How much power would 0.3% grade take away compared to 0% grade?

Thanks!
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