If you buy the 5.7mm, you'll also be buying a reloading press before too long. It's pretty expensive, around $0.50/shot. In terms of terminal ballistics, I've heard mixed reviews. It's got a lot of energy, and it penetrates well. In fact, some say it penetrates a little too well and is prone to over-penetration. It's a good round, but it isn't something I would carry. There just really isn't enough info out about it yet.
This is actually a sweet shooting pistol. The Pakistani Air Force cops use these. A couple of years ago we hosted a competition they attended. I was smoking targets at distances 3-4 times what the average person can hope to hit with a GI M9.
The military loading, designed to defeat body armor, is not available to civilians in the US.
You are correct, but having fired a few of this I can tell you it is an amazing round. I'm grateful that they aren't available to civilians!