The rescue I volunteer with and m local dog shelter USE and RECOMMEND Gentle Leaders.  I have always been impressed with ALL Premier products.  They are humane , readily available and somewhat easy to use.

 The Gentle Leader does require proper fitting.  Your dog trainer, vet or vet tech, or maybe even a sales associate at the store should be able to help ensure this.  Their is a training pamphlet and DVD in most packages to help the owner and dog become accustom to the feel of something around their nose.

 My service dog uses one when she's working. 

NO IT'S NOT A MUZZLE.  The dogs can...