In my experience, these types
of leashes a.) tend to cause dogs to act more aggressively and to pull hard on the leash; b.) are more likely to trigger a fight with another dog since the dog that is straining at the end
of the leash looks like it is in attack
mode; c.) tend to be purchased by lazy and irresponsible dog owners who do not train their dogs to obey, and who tend to spoil their dogs, causing more aggression and bratty behavior; d.) undo most
of the important aspects
of your obedience training and leadership over your dog, especially obeying around distractions and coming when called, and over time they teach your dog to charge after other dogs, animals and even people; e.) are hard to control once the dog is at the end
of the line, and can get caught in the leashes
of other dogs, increasing the potential for a biting or attack incident; f.) do NOT cause the dog to get more
exercise on the walk; g.) can cause a dog to run away from you, because if you accidentally drop the leash handle, many dogs will run from the plastic handle «
chasing» them from behind and that could cause your dog to run into traffic and die; h.) have resulted in injuries to dogs and owners.