A year ago. I needed a backup flash so I started looking into flashes and I found the YN568EX. It supported basically the majority of the features that my Canon 580EXII had except for master IR and auto thyroister mode. Which I could care less about. I have since bought a second YN568EX for use.
The first issue I ran into was on my first YN568EX that I got. There was an issue that existed in the 2012 models of the flash but has since been fixed since I believe May 2013. This means that if on a Canon 60D you tried to take a picture before the flash had a fully charged capacitor it would lock the camera up and thrown an err20… I about had a heart attack when this first happened. I thought my camera was dead. A simple reboot of the camera will fix the issue. The work around was I would just listen for the ready beep before firing the flash again. Issue would come into play at weddings or events where the beep would be very distracting. The second issue I ran into was the door on the newer version of the flash. There is a documented issue with the newer YN568EXII. It seems in the newer date YN568EX it may suffer from the same issue. From a small fall the door broke on the new YN568EX. I easily got the door replaced for 5$ a door from china.
The YN568EX was the first flash from China with HSS. it can sync up to 1/8000. although remember this will significantly cut the flash power so really it is not that useful at that fast. If you add this in combination with the YN622C you get a useful combination in fast moving off camera environments like weddings. Also you are able to do HSS to knock the sun some. However to really make this useful I feel you need at least 2 flashes. I put them on a phottix multibom 16′ when outside. It works quite well.
You have all the normal features you would have with a canon flash. Like full E-TTL communication. You can adjust the FEC from camera with a quick nudge of the arrow left and right. Left for a lower power , right for a higher power. Normally when bouncing flash I need to be at about +1 fec to get the proper exposure. This is not much different than the Canon 580EXII which I have to do the same some.
The main feature the flash is missing is an external battery pack port. This is not a deal killer for me but some people it is. Also they decided to use a 2.5mm sync port instead of a 3.5mm or PC. This sort of makes it tough for those who have widely used PC cables, or the main new way of 3.5mm mono plug.
One of the positive features is also the IR and popup commander slaves. That accepts both Canon E-TTL and Nikon i-TTL signals. This is very useful because on weddings my other photographer normally shoots Nikon so when we needed an extra flash I was able to do an i-TTL slave for them.
In practice the flash performs really well. I have actually used it the same if not more than my Canon 580EXII. I really like the beep in non sound sensitive locations. The main settings are quick to change like FEC and zoom. It sorta is tricky remembering how to switch the channels and the group in i-TTL or E-TTL slave. The interface in regards to changing settings could be clearer. Also the custom function names are cryptic.
Over all it is a good flash for the price. The build quality is ok but not extravagant. It performs well in use. I would suggest it to any one who is looking for an entry level TTL flash with HSS. The big negatives I found is that enough bugs were not worked out, causing one of my flashes to fail on my Canon 60D. Instead of shipping it back which would of cost a ton I ended up waiting for the bug to be fixed and buying a new one.