I actually have one of those, and it's great. The spring keeps you from being pulled over, and the dog is able to run alongside. There is a little plastic tab that attaches to the end of the spring so that if there is a problem the dog is released pretty easily. I used mine for years until my dog got too old and we never had any problems.

On the other side, I had a friend who rode and held his dog's leash. The dog got distracted and pulled him off. He ended up with some brain damage because he didn't wear a helmet.

Springers are awesome.