Practice, it allowed me to use a flash old Metz in Slave I was thinking more to serve me and yet it is compatible and it works very well. The "Remote Control" is also nice especially as the system passes all the functions of canon 600D. By cons, still no instruction in French, it can be found easily on the web, but however it is fairly intuitive so it's OK. I'm very happy and I do not hesitate to recommend it.