Got my Di-866 today from Honkers, ordered & paid on eBay Tuesday AM this week, that afternoon I received a note saying the unit had been despatched, it arrived today, better service than most Australian suppliers. I paid $298.90 including free post from eBay seller hkbns-australia (far cheaper than the Canon ST-E2 remote transmitter.)
Build quality is good, almost as good as the 580Ex, although the hotshoe is plastic rather than the metal item on the 580EX. The plastic finish is slightly more glossy than the 580Ex making the unit look a little less classy. A small minus on the non metal hotshoe compared to the 580EX.
Unit zooms as does the 580EX.
Unit swivels and tilts as does the 580EX.
Used as a slave flash the Di-866 worked first up, no problems. I have yet to test it as a master.
Auto modes support ETTL.
Quick userguide supplied is sufficient for most use, full user manual is supplied on CD.
User interface: Canon could take some lessons from Nissin, the Di-866 menuing is simple and intuitive once you are aware that there are sub menus that activate on pressing the Set button for 2 seconds. The 580EX is a nightmare in comparison to set up .... BUT, most of the 580EX functions are easily adjusted from the Camera (although not all Canon SLR's support this function), where as the Di-866 doesn't support this feature. The display autorotates when you swing the flash 90 degrees.
Vignetting, there seems to be slight vignetting at the 24mm (on Full Frame) end on the Di-866, can be remedied by using the wide flipout. This probably wouldn't be an issue on a crop sensor.
Manual mode is pretty well the same as the 580EX.
Multi flash is similar to the 580EX.
Catchlight pullout is similar to the 580EX.
Carry case is on par, but lacks space for the stand.
Fill Flash: the Di-866 has a small variable power fill flash which can be selected if the main head is swivelled for bounce. It took me a while to work out that fill flash doesn't fire when using the test button, which made me think the unit was faulty at first.
Di-866 has a modelling mode, high speed sync, first or second shutter sync, exposure bracketting, exposure compensation, auto off (adjustable) & screen shutoff after 8 seconds to conserve power.
I'm pleased with the unit so far, hopefully I will get a chance to try some comparison shots and post.