The Kenko worked fine on my 7D. But, it is incompatible with several lenses with my 5DIII and the latest firmware, causing the camera to crash, requiring the battery to be removed to reset. The same has been reported by others. Do NOT get the Kenko.
5DS R, 7D II, EOS-M, Powershot G3 X, 300/2.8 II, 1.4xTC III, 2xTC III, EF 1.8 STM, EF 70-200/4 IS, EF 24-105, 15-85, 100-400 II, Sigma 10-20, Sigma 150-600mm C, EOS-M 18-55, f/2 22, 11-22