Leashes that are attached to a head collar (Snoot Loop, Gentle Leader, Halti) SHOULD be light with small light weight snaps, NOT standard leashes that attach to a dog's collar. Many times a dog will resist and "fight" a standard large snap and 1 inch leash as it swings around when attached to the dog's face. The weight of the snap is disruptive and uncomfortable. The lighter weight clip results in increased comfort for the dog during training.
For safety a 2nd leash can be attached to the dog's buckle collar or a back or front attach harness.