use pulling collars on my saddles. Oh, and just for information, the one in that picture is adjusted 9 miles of wrong. If you went to pull something even a little bit heavy with that one, it would ride up and choke the horse.
Pulling collars are just that, breast collars designed for folks that do a lot of pulling with their horses. My brother started getting them when he was working at a very large feedlot and was roping/dragging/doctoring an average of 50+ head of cattle a day. I started using them because I like the look of them but I've also discovered that they are easier to fit to a horse and fit a wider size range of horses too.
In addition to fitting a wider range of horses, they don't constrict the shoulder at all. Their design is based on the design of the collars of driven plow horses. The collar sits along the front angle of the shoulder so it doesn't restrict movement, even under extreme heavy loads. With the way pulling collars are designed, you won't have a horse get the point of a shoulder pinched and quit on you. Plus, I've noticed that if you keep them adjusted properly, you don't have to keep your cinch quite as tight when you're pulling because the collar keeps the saddle in place without rubbing on the horse.
Oh, and since I searched long and hard for a good one that was also affordable, I suggest anyone who wants a pulling collar to look here. pullin collar NG carlos SaddleSmith equine,western items in Patricias Horse Tack store on eBay!
I have 2 of them and you won't find better quality even at twice the price.