Question on tubes and Canon ring flash...

Does it make any difference as far as functionality with the Canon 100mm IS macro lens if I use a Canon extension tube or a set of Kenko tubes along with the Canon Ring flash? Is anyone using tubes with the Canon ring flash and the 100L and which tubes do you prefer? Are there any advantages of one over the other?

Extension tubes have no glass in them and are therefore functionally identical given the tubes are the same length (all 12mm tubes will produce the same result, for example).

The differences between tubes comes down to the quality of the construction and the presence of contacts to allow for auto focus and focus confirmation. I have the kenkos and they are of good quality. The canons are made of metal as opposed to the plastic of the kenkos. Vello also came out with some very cheap extension tubes that have gotten positive reviews on the forum but I can't vouch for them. All three have contacts.

I have no experience with the ring flash.