I wanted one for my Sig Pro but watched too many other guys have problems with the same gun and they often made real expensive .40 brass by fire forming the .357 and you need a cleaning rod and a hammer to get a lead loaded .40 out of a .357 Sig barrel, when you close the slide. And these were gun guys doing this.
My only advise if you really want the second barrel is to paint it a different color on the breach or write .357 and 40 on the breach in large letters, the little stamped ones are hard to see when at the range, and you never want to look into the front end to see how big the hole is.
The .357 in the forty barrels make a funny noise and the bullets key hole into paper and if the cardboard, the target is stapled to, is thick like a wax packing crate it will bounce back at you. No stopping power there. LOL
I decided that I would be happy with my .40 and only have to stock two types of ammo for the one handgun (Defense and target) rather than 4 types. (D&T) X2
Also the .40 seems to be cheaper to shoot.
My problem is with Mr. Murphy. He is always looming and sure as anything the .40 barrel will be in the gun and I pack .357 Sig ammo for a match.
Don't get me wrong I think .357 Sig is a great round and am saving my pennies in hopes of finding a P226 in it used someday.