Canon vs Sigma Macro ring flashes

[dllavaneras]

I've been looking at two different macro ring flashes, the Canon MR-14EX Macro Ring Lite and the Sigma Flash Macro Ring EM-140 DG. I would use them on a Canon 100 mm macro lens. Any particular advantage the Canon has to justify the 150 dollar difference? As far as I've read (which is not much, so please correct me if necessary!) both are quite good, as both have the option to choose the intensity of both tubes.

Is there anything I'm missing?

Thanks in advance,

Daniel Llavaneras
Happy S1 IS owner and future (hopefully!) 400D/30D owner
www.fotolog.com/nano_el_enano