Concept Bikes & Bike Innovation - for better or worse

"DrivEn hits the magic 99% efficiency number at 380W of rider output"

So, pretty much the same as a single speed roller chain :)

Strictly speaking, their system only completely avoids sliding contact at the drive interface if the outer races of the rolling elements are conical, and the cone angle needs to be different for each different driven gear as the apex has always to be coincident with the axis of the driven gear.