If you're shooting sports with the 70-200 (and not more static objects like the majority of kenko users are doing), I would say to spend the money and go with Canon. I had a Kenko 1.4x MC4 DGX and it was pretty terrible for action shots (maybe a more expensive one would have done slightly better). AF tracking was severely degraded on moving subjects. I returned it for the Canon 1.4x II, which works awesome and has very little IQ loss (coming from a pixel peeper). It is attached to my 7D and 70-200 2.8 IS II a good half the time I'm shooting outdoor sports.