I too have used this in the past - problem comes when either you don't have it with you or someone else is around the flock and they don't have it. I've used it more as a proactive training tool, rather than to fight off aggression. I agree, it will deter aggression, but not necessarily...
You did indeed do the right thing (a little pinch on the neck to simulate a peck would have been the icing on the cake), but whether it will make a difference to the next time you go out is another matter. I'd say there are as many opinions on how to deal with an aggressive rooster as you've had...