FROM MY ORIGINAL DC 20 REVIEW - "I also have some concerns about how the dog is going to wear the unit. The Garmin Astro comes with a neoprene vest that goes around the dogs chest and is also attached to the dogs regular id collar. The vest idea is ok (I was real pleased with the quality and the construction) but I hunt in a lot of really hot weather. The last thing my dog needs is a neoprene vest on him when it's 70 degrees. No problem here, it can also be worn on the collar."
The biggest change from the original Astro is in the dog collar. The DC 40 is a stand alone system. Unlike the original DC 20, the DC 40 does not need a vest or a counterweight (ecollar, dummy collar, or any other rigged contraption) to keep it in place. This one change fixes the majority of the problems that we saw over the first season of running the Astro.
The beauty of the self contained collar is that the Astro can be worn by itself.
This change has also fixed a couple of other issues. It was hard to keep the astro in place while running small dogs. There were certain size limitations with the original set up that we don't have with the DC 40 up to a point.
The DC 40 collar strap goes as small as 9 inches and will fit a dog as large as 22 inches. This sizing is going to work for the majority of the dogs that it is directed towards but there will be a few issues. You can get away with wearing it on a dog with a slightly smaller neck than 9 inches, but I would not go much smaller. I would not recommend using it on a dog under 12 pounds from a weight standpoint.
We will see more folks looking to wear it on dogs with necks larger than 22 inches. To fix this all you need to do is purchase an extra ecollar strap and buckle them together.