I chose the Metz knowing that it is essentially a twin flash unit as opposed to a true ringlight. As such, it is considerably lighter and more convenient than any other wireless TTL twin flash alternative. I wanted to shoot a Sigma EX 180/3.5 Macro handheld, so needed the 72mm compatibility, and with the big lens, the light weight is a definite plus. Quality of light was definitely trumped by convenience in this case. In the very limited world of available P-TTL compatible macro flashes, I saw this as my best alternative.
My requirements for macro are unusual, and probably unique. I'm primarily a birder, and wanted a lens combo that would allow both 1:1 or better macro and at least 300mm tele in the same lens. I can get this with the Sigma 180 + F1.7x AFA (306mm).
All I need to do to switch from macro to tele is close the popup flash and manually prefocus the lens to tele distances -- only about 1/4 turn with the Sigma 180. Since the Metz is so light, it doesn't hinder the swing weight or handling much in tele use. I do have to remember to open the aperture up a bit, and I'm still getting used to doing this.
Here are a couple of examples, both cropped and PP'd to taste. These are small Jumping Spiders, probably about 2-3mm long in the body. These were shot with the K20, Sigma 180/3.5 Macro + P F 1.7x AFA, and Metz 15 MS1 in Pentax wireless TTL mode, using AF C to focus, handheld. You can see the twin flash glints in the eyes of the JSs. I could, of course, clone one of the reflections out if desired.
This first guy is on a window screen to give some scale.
In this second shot, I rotated the Metz to give me a vertical twin flash setup. I biased the flash to the bottom, but probably could have eliminated the shadow under the spider by turning the top flash off, but I'm still getting used to all the lighting possibilities of this flash. . .
Scott