We have a 2 year old german shepherd that we have used the chain on. We had to use it twice max and he never jumped up at anyone again. He is a very placid dog and play mate to 4 children between 9 months and 5 years old (obviously never unattended though, regardless of how placid) and using the chain has had no affects on his personality. He is still very outgoing and extremely playful and in no way timid or flinchy to sudden movements or loud noises.
In saying this though, I think when it comes to training you need to use something that suits the dog because each one is going to react differently to certain techniques. What works for one dog, may not work for another.

Papillon, my pups must be a late bloomer, he's 2 and still squats! :shyface: