I had two significant problems with this cord. It doesn't maintain function when you use a 580exII fully locked on the hot shoe. If you only slide the locking mechanism over halfway you can get the synch function but flash wasn't secure. My first shoot with this cord was a wedding. Halfway through the reception the hotshoe on the cord became loose from the bottom portion where it connects to a flash bracket. Bottom line if you are planning to use a 580exII save your money get canon or another brand. It worked okay with my 430ex but after the bracket connecter started to wobble that rendered it useless.