I have used this collar on at least 20 dogs. Many of these dogs had no obedience, bad manners, and behavior issues that required training. The most common problem among the many has been pulling on the leash. This collar will do just what the dog needs in order to begin to end leash pulling and that is to be uncomfortable when it is pulling on the leash. Harnesses, harness leashes, "gentle leaders" and the like are merely gimmicks being marketed to those with good intentions, but lacking in knowledge about leash pulling and other unwanted behavior as well as dog obedience training. This collar is inexpensive, made well from high-quality materials and easy to use if the recommended sizing and fitting instructions are followed. This collar should always be used with the included nylon backup slip collar or some other type of collar. I use a snap-around collar for a backup.ALWAYS USE A BACKUP COLLAR! Pawmark sells a leash extension on Amazon with two snap hooks that works well to attach the leash to a primary and backup collar. This collar is effective as a general training collar for most dogs. I highly recommend trying this collar before spending a lot more money on a conventional metal pinch collar. The size of the collar is adjusted by adding or removing links. This can be a little tricky at first. However, there are videos that demonstrate how to do this properly. After a couple of tries, it is not hard at all. If you are unfamilar with pinch collars or have been exposed to the negative propaganda about them from the Dark Side, you should know that these collars are not painful nor do they injure the dog in any way if used properly. But, NEVER LEAVE THIS COLLAR OR A PRONG COLLAR ON A DOG FOR DAYS!! This is really a bad idea. I have read some of the less than positive reviews concerning this collar. Some of them are irrelevant as they refer to a different collar - with pictures included. Others are in the category of those unique situations such as dogs with very long coat hair, and dominant or aggressive dogs. This collar is probably not going to be as effective as a prong collar for specific special cases. The collar is a great first collar to use for most dogs. However, like other collars and tools might not be effective for some dogs compared to a prong collar. I use a prong collar for foundational obedience work and then switch to this collar when moving the dog to an electronic training collar. The small collar size is suitable from my experience for dogs up to 50 pounds or for dogs with small necks. If it is the case that you have to use less than six links for a dog with the large size collar, I recommend using a small size and adding links. You do have to take some time to read and follow the instructions and watch the videos on how to size and use the collar - especially adding or removing links.