For initial thoughts, as a gun nerd and overall mechanical geek, this is a thing of beauty in design. The idea that in about 30 seconds you can do what is essentially a field strip and have the entire fire control group out of the gun swapped into a different size grip and slide on any caliber top end you wish and still only "own" one gun. Seeing as the FCG is the registered part you can have as many grips and top ends as you want. There will be a video of grip change in the next post because they have done so much more.
For my initial test, I went to my old standby; 15 rounds at 15 yards in 15 seconds. Think extended Bill Drill. For that test I used the Sig ammo provided 115Gr FMJ, Independence 115Gr FMJ, Freedom Munitions 124Gr JHP, American Eagle 115Gr FMJ, Remington 124Gr Golden Sabre +P, and just for fun Tula 115Gr FMJ.
So today I wandered out to the range (we have a 25ydsX25yds three sided berm pushed up in our north pasture) and tossed up a target and started shooting. Interestingly the ejected brass all ended up in a pile about 6 feet to my right, except the nickel plated brass of the +P. That stuff ended up about 3 feet behind my right shoulder.
Next up, grips and what Sig has done with them.