Assuming the technology is real, the cell can in fact "take energy from nature" and convert it to electricty, it would take days or weeks to absorb enough energy to charge a phone. A phone takes 2 amps of 5 volts to charge, 2 amps is a lot of current to generate. I watched the video, and I couldn't help noticing the voltage generated is in the range of radio noise picked up by our bodies. It also took 3 minutes to charge up that small capacitor, so current would be very small.
Yeah, the ROI could be 20,000 years for all I know. But according to themselves it seems to be under 1,000 years which probably is attractive to some people.
Pay 1200 euros, get a FREE cup of coffee every third year for the rest of your life, I wonder how many idiots would fall for that...