I was extremely please with the results from the Canon Ring Flash but our to its cost (£500 ish) decided to repair my Sigma, which I did. The main difference between the Sigma and the Canon is with the Sigma you had one ring tube and this gave very flat lighting. The Canon had two half ring tubes and you can vary the power between the two tubes to give some modelling light.
I happened to be looking again at ring flashes just before Christmas and found the Yongnuo Macro Ring Lite YN14EX had an almost identical specification to the Canon, i.e. guide number and gettability of the tubes AND was about £80. I have another Yongnuo flash that I use as a slave flash unit and very pleased with it. The build quality is obviously not quite as goo, but good enough.
Sue asked me what I wanted for my Birthday and I told her about the Ring Flash.
So here are some very quick tests.
The ratio of the two tubes is in the form A:B. So 1:1 is both A and B Tubes at full poser. 8:1 is Tube A is 8 times the strength of tube B. whereas 1:8 is tube B is 8 times the strength of tube A
In these photos A is the left hand tube and B the right.
I am Very pleased with the tests and looking forward to trying it out 'in the field' :)