I haven't updated the firmware, everyone I know is Apple only, so that will take me a while.
1: It is not a clone, it is slightly bigger than an ST-E3-RT.
2: The buttons are all easier/looser than the ST-E3-RT, I find the original ones too stiff but they never get rubbed or knocked to a different setting, I suspect the YN-E3-RT will be the other way around.
3: Group Mode on my 1Ds MkIII's works right out of the box.
4: Second curtain sync in M Mode only and with a maximum of three groups works straight out of the box.
5: The shutter release cable works badly, it triggers the camera but not the flashes! With the ST-E3-RT all flashes are triggered when the shutter is.
6: There are no Personal Functions as per the ST-E3-RT.
7: The AF assist beam works very well on my 1Ds MkIII's with my crappiest focusing lens, the 50 f1.4. The beam pattern is well lined up for subject around ten feet away, get closer and the beam pattern gets progressively higher in the frame. The beam pattern is quite broad, certainly much more than a center AF point only deal.
8: Range, it is the same as the ST-E3-RT, effectively. In fact it can fire a 600EX-RT from slightly further away than an ST-E3-RT but it doesn't maintain radio contact anywhere nearly as reliably as the Canon version. Once they both lose contact the ST-E3-RT will reconnect from much further away. All in initial trials. Do not buy a YN-E3-RT based on longer range.
9: The pouch is much thinner material than the Canon one, not good or bad just different and obviously cheaper material.
10: I got the two trigger/remote cables with mine. A nice included extra that is a $50 option with Canon!
11: Mine came with batteries in it. That would have been nice but for the fact that even though it was an unopened box the On/Off switch (remember I mentioned that?) had been knocked to on, so the batteries were dead and my unit had been on the whole time.
12: HSS works exactly as the Canon does.
13: Sync at close to pre RT speeds (the infamous losing one stop of shutter speed) works exactly the same as the Canon system does, at closed down apertures there is a slight shutter shadow, at wide open apertures there is not.
14: HSS works perfectly in Group mode with full selection options.
15: There is some play in the hot shoe mounting when it is locked down, no biggie, just a small quality control oopsie that illustrates the cost advantage.
If you have a pre 2012 camera and 600EX-RT’s this thing is a NO BRAINER, get it, it is vastly better than the ST-E3-RT for you. If you have post 2012 cameras then it is a good cost saving and the AF assist light, if you need that functionality, is a good bonus that actually works, it isn’t a tick on a spec sheet useless addition.
I have the YN-E3-RT and the ST-E3-RT, I thought I’d sell the ST but at this point I won’t because I need the remote shooting function to fire the flashes too, maybe my unit is defective or maybe it is a firmware issue. The ST-E3-RT is much better made, it is more solid and robust feeling and the buttons and dial, though a little too stiff, are a better compromise than the looser YN-E3-RT ones.