I ordered the twin pack as I have two jack russell's one of which has "borrowed" one of these style collars whilst on holiday in Devon and it was instant. So I bought them after much consideration. They are not cruel, they work, more or less instantly!!! My dogs are aged 7 & 8. These particualr collars give off 2 sound warnings before the zap, the younger smaller dog didn't get to be zapped, she had learned from her experience on holiday. The older dog (who thinks she is royalty) had to go that 1 step further and ended up being zapped. I have only had to use them once. Who says you can't teach an old dog new tricks, well you can and these collars are a brilliant tool to teach them that they DO NOT have to bark at every passer by!!!