Two pros may have two very different triggers but still manage to play at that level because they have tailored their technique to their physiology, reactions, and hand-eye coordination. And, this is why there is no universal technique.
Clubbies should experiment with different techniques until they find one that works for their ever weakening shoulder, eye-sight, and diminishing reflexes. Don't forget bat weights either.
Indeed...bat weights, one of the oldest parts of the game, remember a sports shop advising how to choose a bat. It's just taken years for the penny to drop! :-)
Reading this thread with interest, having worked on correcting technique to prevent over balancing for about 4 years it is starting to work...
So...for some players they naturally have a good set up to allow(as has been pointed out by meany on this), a level and still head, balanced feet and two eyes looking at the ball
For some others we need a trigger to get into the right position.
Personally I move back and across a bit and put my weight on the back foot, that helps me keep from overbalancong to the offside, also I try to open the left shoulder towards mid on. I'm sure there are others with the same problem it's pretty common.
So the trigger just helps get in the right position in the first place.
Can't overestimate thou using the right weight bat. Maybe it is the most important part of batting? That and really watching the ball.