There is another option not and that is the Strobeam EID500 which is both mains and battery powered. I bought the 2 head kit with single battery at SWPP the other week and am impressed. The battery pack is about the size of 2 Canon 580 speed lights and unusually gives 100% power to both heads. At t0.5 the flash duration is 1/8600s. The only downsides are that you only get one 3m long cable and a short coiled cable so, until longer cables are available separation distance of the 2 heads is limited. They are only available from Viewfinder Photography and they are having a lunch day on 11 Feb 12 with special offers on.
