The YN600EX deserved theoretically 5 star - would if the (quite brazen) advertising message of YONGNUO actually agree: "This flash YN600EX-RT is exactlly same as the Canon 600EX-RT flash's Best ...". In practice, however, is not quite true, may still not ... The good news: The flash functionality can convince at the first test, ie the YN600EX-RT works comparable awesome as the original. Whether in fact the full guide number is achieved and all the latest technology such as the Canon function, I will gradually have to try and then report. And the appearance fits, ie the YN600EX-RT is almost indistinguishable at first glance from 3-4 times as expensive 600EX-RT Canon. On closer inspection, then fall to quite a few simplifications and even small size differences, but they are insignificant in practice. For example, the lock was saved when turning mechanism which is superfluous anyway. In addition, the plastic is not quite as stable and high quality as the original from Canon. But that is hardly noticeable except when battery lid but flexes slightly when closing. Overall, however, fits the quality, I would say 90% of the original. Now the bad news: The YN600EX-RT is due to a bug in the firmware a real "battery eaters" - even when switched off! In contrast, only helps to open when not using the battery cover or completely rauszunehmen the batteries. Now YONGNUO advertises that you can upgrade the firmware via USB and provides a newer firmware version incl. The appropriate PC software and instructions for download ([...]). And reportedly also the "sucking" the batteries will be turned off by this new firmware (v 1.81) in addition to other small malfunctions. Unfortunately, the firmware can not currently upgrade with current technology because the software (for WIN XP / WIN-7) is still recognizable in the beta stage and there is no working driver for 64-bit operating systems, ie the YN600EX-RT can not be addressed. But what BS is nowadays no 64-bit and who still uses an XP in 32-bit version (which came on the market 14 years ago) ?! I could not find a suitable computer for a firmware update at least so far, although I have even nearly 10 years Equipment excavated and tried. And the brief Manual (English / Chinese) still contains some errors. My conclusion: Unfortunately, not yet fully developed, although the actual flash functionality can already convince and - if tested - certainly comes close to the original. Therefore, currently only 3 stars and no purchase recommendation. Better to wait a while until the unit is out of the beta stage and then maybe actually deserves 5 stars.
UPDATE 02/02/2015: Now have an upgrade to the latest firmware 1.8.1 performed (using a 32-bit Win XP computer, built in 2002!). From FW 1.8.1 the YN600 of today's conventional 64-bit WIN versions via USB is approachable, which is a significant advance for future FW upgrades - and there will probably be quite a few (have) ... The new FW 1.8.1 are indeed fixed some minor bugs, but not the really serious bugs in the power management system, ie the batteries are still "sucked" and their capacity is constantly wrong / displayed swaying with corresponding consequences, etc. It turns at all the question of whether these errors as simple can be remedied by software upgrade - or not but also the hardware / circuit needs to be changed. Then only helps an exchange ... Therefore, it remains at the 3 stars - despite very good flash results - and at the recommendation of the technical "teething problems" to be seen at YN600 firstonce!