I have a very old EM-140. It needs a firmware update, which I think Sigma will do. Mine does not work consistently with Mup on later cameras, and also inconsistently in Autoexposure mode. I only use it in Manual mode for work on a copy stand. I should get the Mup problem fixed, though.
I think Mup worked with the D2h I was using when I bought it. It stopped working with either the D200 or D300. Sigma told me they could fix it (that was several years ago now).
Just to say my 5+ year old unit, made before the D200 came out, I think, may not be representative of the feature set compatibility of new units.
Seems to me that no ring flash would make a good "general purpose" flash. In general, you want the light coming in at the most extreme angle (to a reasonable extent) as possible. That is one of the benefits of a hot shoe mounted flash, verses using a built in pop-up flash.
Any ring flash, by design, will project the light almost parallel to the optical axis when used at "normal" distances of more than a foot or so. You may have considered this but I have to throw it in to make sure .
It is also not a very powerful flash but Brian covered that.