An independent cross-over study by Schüling et. al. (2013) commissioned by the German ministry of Social Affairs concluded that, with respect to the VGK-Go!, (commonly known as VGK):

“The VGK is the only modern knee joint not electronically controlled and in terms of functionality, it offers an equal value spectrum as electronically controlled knee joints.”

“Both … as well as the VGK showed equivalent functions in regard to gait dynamic and stance safety compared to the electronic fitting.”

“Multiple participants of higher activity class show equal and superior results with the VGK.”

“Participants of lower activity class had results with the VGK not essentially worse than with electronic joints.”

All citations taken from:
Knee Joints with controlled Flexion Damping for Transfemoral Amputees in a Clinical Cross-Over Study: C-Leg, Rheo Knee II, VGK, Orion: English Edition 2013
by Stefan Schüling, Markus Hildebrandt, Kerstin Tiemeyer

Available in any bookstore under ISBN 978-3865232403, e.g. online at amazon.com or directly from the publisher’s website.