I have one. I use it rather more than I had expected. It is a specialty device, really not suited for anything other than macro work. This is for a couple of reasons. First, it's a pretty bulky contraption. Second, and probably more importantly, it is not very powerful. That may seem like a problem, but for its intended purpose, it's not: by definition, macro work is done at very close distances, so adding a lot of power to a macro flash just increases the cost and weight of the unit.
The unit works quite well, with really only two drawbacks. First is the manual, which is pretty bad. Even as a reasonably experienced user I found the manual pretty hard to use, although I did figure it out in the end. Also, it does seem to have a limitation on how far it can dial back the flash tubes. I find that every once in a while I get a pretty drastic overexposure when I'm too close and have the aperture wide open - my impression is that the unit has a range of full to 1/32 power or about five stops. Well, no - I just checked the specs and it goes down to 1/64th, so perhaps this is just cockpit error.
_____ Brian... a bicoastal Nikonian and Team Member
My gallery is online. Comments and critique welcomed any time!