Since I'm already a previous owner of the Speedlight 580 EX II, I have some time to prepare my accessories on yet gained the Speedlight 600EX-RT. The first thing I noticed is that even the diffuser, which I have used when Speedlight 580 EX II, although with some effort fits this model and even more stable it is seated (I speak here of the round diffuser, which looks like a misshapen yoghurt pots ) the second, and for that I am grateful Canon is if slowly the battery runs low, there is no over-exposure more but it appears that the battery is empty and nothing else happens. The Speedlight can be set up as a slave and responds wonderfully with the 580. Could not be better!