Throwing another rock in the "headset/hand signals pond" - To insist on headsets is great but at the same time we should be clear how instructions get to the tug driver from the Talkout assistant. It's normally done by hand signals! To date, the safest pushbacks I've experienced are from towbarless tugs without a Talkout assistant, talking directly to the tug driver. Cutting out the middle man gives a measurable increase in safety (figures from another bit of the company - many tens of thousands of incident free pushbacks). The next best is a well trained crew sticking to standard procedures working well within their language limitations. Then it becomes hand signals. Unsafest of all is headsets, poor grasp of language, non-standard and interrupted pushbacks on late departing aircraft.
PM