The first of the Canon tubes has arrived.
To look at very similar to a Kenko tube, almost identical, similar leaver.
The leaver streangth spring is about 160-180g so 2-3 times as strong as the Kenko version.
The main difference is the amount of torque required to mount and dismount the lens. It is a lot less likely accidental movement of the leaver would cause the lens to unlock (I hope) as this would require considerable torque to be applied at the same time.
As has been observed by some on this thread the Canon tubes lockup tight with no obvious rotational or axial movement that I saw in the kenko tubes.
I think if you just use these Kenko tubes for the occasional shot you are unlikely to have a problem, but if you will be using a tube assembly all day, handling the equimpment a lot, different orientations, use of the stopdown preview, carrying the lens, and even with a smaller lens like the 100mm macro, this could be an issue.
Of course I can only comment on the Kenkos I have, not on others. I suggest care if the mounted lens at all loose.
Thanks to everyone for their input.