I have used an ecollar twice on my youngest female, and a trainer used one once on both my girls.
The very first time the ecollar was used on my girls a professional trainer was doing snake avoidance training. Belle, my oldest, was one year old when we trained her on rattlesnakes, water mocassins, and copperheards (I live in Central Texas and we see those three poisonous snakes from time to time). It took one zap (and timing was critical) and Belle now avoids (she scents rattlesnakes from 50 ft easy) these three snakes. Same thing happened with Halo (my youngest), only we did her at 6 months.
The second time I used the ecollar (I bought a Innotek for home training) was to teach Halo to stop jumping on my windows. I had tried everything else and I was terrified she would break the glass and cut herself bad. So, I hid in the house and put her outside. As soon as she jumped on the window zap (started with the lowest setting and worked up) until she got down. Only took a couple of times and she got it. Timing was important and also I did not want her to see me as I wanted her thinking the windows were bad news.
The most recent time I used the ecollar was on Halo for a reliable recall off leash. She was 3 years old this time and she was well trained on both come (come to me on first call and sit in front of me) and here (come to me on first recall and check in, no sit required) on a long leash. We used the ecollar as Halo would get off leash and forget everything and take off running. We wanted to be able to hike with her and Belle off leash in wilderness areas, take her to the beach and let her off leash, etc. We also wanted her to come back immediately when called. Well we got the opportunity last week to test this on a vacation to the New Mexico mountains. In preparation I bought a TriTronics collar with a 1.5 mile reach. We hiked about a mile to wear her down a bit (she was on leash) and when we got to big meadow we let her off. It took one time (I said here, she didn't respond immediately, so repeat here and zap, as soon as she looked at me and started my way I stopped the zap). After that she knew I could still reach out and touch her and she was dead on with the here command any time. I would call here and she would come flying to me.
Hope some of this helps as I am a firm believer in ecollars for the appropriate things. I only use them though in life or death situations or to enforce an already learned command.
Bev and the Pointer Sisters
PS - I also tested both my ecollars on myself first too.