Just get the Canon's.I have Canon and my son has Kenko. Kenko feels a bit less solid, but I doubt you´ll run into problems. If you plan to use heavier lenses, I´d feel more comfortable with Canon though.
I've got a 12mm & 25mm and it works 100%
I've never used the Kenko's so can't comment on those but it does seem that value for money is a factor.