The first model, I have to change again because the battery door was broken - this problem is from the date of the beginning of 2014 but well resolved. With the current model (manufactured 6/2014) but I have problems with bounce flash with ETTL: the images are too dark! Direct flashed it is much brighter. At the performance, or any incorrect settings is not - this is a problem and is discussed in the relevant forums. If you compare the ETTL-measurement method to "integral" to alleviate the problem. And it seems that the recent lightning no longer have this problem - at least flashes of 11/2014 not seem them to be affected. Maybe the model is now (finally) mature.
The date of manufacture can be found incidentally on a sticker, if you turn the flash head to the side.