Wedding was yesterday and I'm currently downloading images.
With the overcast weather yesterday I didn't use the flash once outside. I used it in i-ttl mode for one signing the register shot (god I hate those photos), a couple of indoor venue/detail shots and it was perfect as a fill in flash.
Then for the evening, the venue we were at has an incredibly poor dance floor setup with regards to lighting, or should I say lack of! For this I had 4 Yongnuos off camera, one in each corner of the room with a transmitter attached. Then had the master controller on the camera and it was perfect! Fired every single time (100ish shots) and I found the controller to be fantastic. Started in Manual control but switched over to i-TTL with -2/-3 compensation and again it all looked great on the back of the camera.
So for our very limited use, I think they are fantastic. The only let down is that they can't be used as a master flash without the transmitters, and then there is no control over off camera flashes independently. That may be incorrect but was my understanding.
My usual setup is off camera flashes set to manual, then on camera set to ettl/ittl with some flash comp. This will work fine providing there is a transmitter on camera with the flash too.
For me, they are a great buy and a similar setup would be around three/four times the price if it were Nikon/Canon branded.
One thing that has struck me and it's hard to explain or prove my point, is that the shots I took yesterday with the flash didn't really look like there was flash used at all. More likely down to Nikon v Canon (as I've recently switched over to Nikon). I may be wrong here and will need to look back at similar shots from weddings at this venue last year to compare.
Edit : My only annoyance is the fit on the hot shoe. While its secure, it does seem to move around a little more than I'm used to. Its never going to fall off or come lose but there just seems to be a bit of play in it.