Last time I got my wet hand on a live wire I couldn't move so good, either. But it was far from a positive experience. Next thing they'll do is waterboard cattle into submission.
I have one. I use it.
I won't risk having a stomping, kicking cow break my hand or arm again if I can help it - but I'm also hoping that current breeding strategy will eliminate some of the bad udders I've had to deal with the last couple of years.
I've hooked myself up to it - it's NOT that bad. Certainly nothing like getting popped by a good hot electric fence.
Cows that I've used it on - twice a day for 4-7 days sometimes - are no more reluctant to come up in the chute than they were before. I don't think they necessarily regard it as any more unpleasant than just being in the chute.
But, back in the day, I have grasped a rectal electroejaculator probe in my wet hand and turned up the voltage - you could feel a tingle but nothing too bad(though I don't know how I'd react to one in my rectum.).