Well, this won't actually be a review because you can already find that here, and I highly recommend reading that first. I just thought coming up with some extras.
So, first things first, ordering and packaging. Of course you can find them from big suppliers like amazon but I got a pair from the official ebay store, payed 94$. I ordered them on 23 November 2012 and even though they appeared as shipped the very same day I received them on 15 January 2013. Almost lost hope for them but can't put any blame on the sellers, holidays were in between and a lot of bureaucracy. Got a pleasant surprise right at the post office though, as the package was marked as a gift and priced for 30$, great for dealing with customs.
Packaging is quite remarkable. First, there's the bubble wrapped envelope. Inside is an "original" fancy cardboard box, inside it a blank one with just a "tips" label on it (read the manual, don't use the units on a high voltage flash, it's OK to torn off the protective film), then comes two individual bubble wrapped bags protecting the tranceivers and an user manual and even a quick start guide. Even more, when I opened the battery cover I found a silica gel bag used to protect from moisture. The mentioned protective films protect the focus assist lamp and the top surface of every unit. I admit, I'm very impressed with the level of care these guys put into such a cheap product and yet so feature rich.
Unfortunately the so called documentation is quite hard to read as english is definitely not an often spoken language at Yongnuo, an extra reason to read that link I was talking about in the beginning. But that's hardly a problem with the amount of online support these days. The real problem I found was the fact that the hot shoe connection to the camera is not properly aligned as both units were having a slight left twist when mounted. It's nothing major, it doesn't even affect the focus assist lamp's aiming, but it's there non the less, for reasons that I can't understand. I thought about opening up a transceiver to get a look at the insides but is seemed it needed more than just unscrewing the obvious 4 screws, and that "more" I could not find. That also killed my hope that the misalignment can be somehow fixed.
The focus assist lamp is implemented through a laser diffraction grating that gets the job done in most cases. The limitation comes from a narrow central spread of the pattern and that fact that at close focus distances that pattern doesn't even cover the center focus point but stays above it because of the lens/transceiver parallel axes. That's not quite a big issue as it can be fixed if using single spot focus moved somewhere inside the assist projection pattern.
When it comes to weight, one empty transceiver is 76g, adding a pair of enloop 2400mAh got the scale at 136g. The enloops are quite an overkill for the task and regular batteries of cheaper rechargeables will do just fine and cut the weight a little. A nice surprise came from the battery compartment. Instead of the classical design where a spring is mounted at each end, here the springs rest inside the unit and metal pads at the insert/extract side. This makes the use much quicker and easier even though adds for a little attention to look at the battery marking.
But all this aside, what about using them? Well.. it can be as transparent as using a normal optically remote Canon flash or as complicated as other radio TX/RX offers with little buttons, lights and combinations. Point is.. it does it all, or the most of it at least. Am I happy with the purchase? Actually I'm waiting to get some money for another pair so I can use 2 off camera flashes.