I use a 560-TX to trigger multiple 560-III speedlites, in the hotshoe of a gripped Bronica SQ-ai. The only "problem" is getting the trigger into the hotshoe, since it is only grooved for a center pin, while the transmitter has multiple off center pins which have to be pushed in as you are putting in the transmitter. I had concerns about voltage, but found something somewhere on the internet that reassured me enough to go ahead and try it.
Edit: Yongnuo triggers and flashes