How does that "blocks 100 percent of the radiation emanating from cell phones"?
Rounding up.
To be fair, the physics behind such a thing might be solid-ish, if overhyped. Headphones
may serve as an unintentional antennae with regards to the phone. Moving the nearest metalic component away from the head can in my opinion
reduce received doses, as the intensity of a field weakens with the square of the distance (assuming a normal pattern).
edit:
The 100% is obviously bollocks. You still get the full dose where ever you put your cell phone (pocket).