If the voltage is appropriate, it can potentially be nothing more than startling. My concern though would be to thoroughly research the product, as many that I have seen are cheap Chinese brands and its a small niche product so you aren't bound to find many reviews. As far as I know, there is no regulation or real research on the proper amount of voltage for cats. Testing it tied around your wrist for potency and ensuring it can't operate continuously would be important self-checks, and ensure w/ your vet that the cat is healthy enough to tolerate the shock provided.
BTW, I have personally worn a dog shock collar, although w/ a turtleneck inbetween it and my skin since I was chicken and that more appropriately mimics a dog that has fur between it and the skin, and it is NOT that bad. I think a lot of people are concerned that its the same intensity as a taser, and I can assure you those hurt so bad, and at least the one I wore was not that strong.
Cats do learn from association, and just as a cat can avoid a litterbox due to associating the box with discomfort from urination, a cat can surely learn to associate a counter or something similar with a short brief zap. It would in fact be more effective than a spritz of water since there is no concern of being associated with the punishment.
The path of least resistance though would be to simply use a product like the SSSCAT which doesn't have any safety concerns and doesn't require the cat to carry around a bulky and uncomfortable device on its neck.
For the yard, a passive system would also be recommended, and there are various options for cat-proof fencing solutions.















call it mean call it what you may but i would much rather have my cats safely in the house then for

