It works. You can also tie something around the middle of a cat like a teatowel and it has the same effect.

I used this to train a cat not to walk on my desk. Kept a teatowel and would do this every time for for a bit when ever it walked across my keyboard/papers while I was working.

Not sure if was ethical... Cat didnt seem in any discomfort, just annoyed it was stuck there. Was a while ago so not sure but seemed to train it ~5 times.

For adult cats, you might want to also support their weight instead of holding them up just by the scruff. It definitely works though.

Yes. Any vet will tell you: it works.