If Im doing the preg checking or AI'ing. I'd rather not use it in those situations. But sometimes if the facilities aren't ideal, I believe a little zap decreases the overall stess of cow vs being handled and handled and handled to try to move her through the system.
Grab it quicker working stockers and calves that are backed up and made up their mind they aren't going to go forward. Less comotion to get the other cattle worked up.
Yelling and hollering is much worse than a hot shot. So is sitting there prodding and prodding them and such. Set up the alley to not interfer with their advancing, a little zap if they won't go and it should be a done deal. No body gets real worked up. I don't like pregging afterward because they are little more tense, so I'm not saying zero effect, but a good option at times when they aren't flowing well.
I've been zapped by them. Some store a charge in them. Got hit in the cheek once by one sitting up along the alley. It got my attention, but it's nothing like an electric fence.
A tool that has its place when used and not abused. Same as prods, whips, paddles, and dogs.
Edit: i get the far majority to advance with just using their flight zones, talking to them and tapping their back end.