I recently bought one of these and 2 receivers for my 580 ii speedlites. The system does basically the same as the Pocket Wizard and Radiopopper equivalents. ie. radio frequency off camera ETTL flash control. It can control 3 groups of flashes independently up to 100m. Allows HSS, FEC and 2nd curtain sync. So far it has worked flawlessly. It is well made and everything can be controlled from the camera. It has 3 modes (ETTL, manual and Ratio).
I have a few bits and pieces made by Phottix and they are all really good. They have a nice solid feel and certainly debunk the "cheap Chinese" myth.
A question for Colin. If I use ETTL off camera and flashes fire though an umbrella, is the ETTL metering still effective? I know the flash fires a predetermined pre flash and then measures it and calculates the correct flash intensity based on that measurement. I just wonder whether this preflash is "interfered with" by the umbrella or not.