Captiva,
For those whom enjoy shooting 5.7 mm systems, more power to them.
However, within the LE\Mil world, its been known to be non-performing for our needs and its real world application. While various tests will illustrate the cartridge's ability to perform within the testing medium, there is no real world data supporting awesome ability as a man-slaying cartridge. There is information available, from those directly involved, regarding its performance in a different respect.
Periodically, it will pop up, and now and then a department will evaluate it for use; there are even some departments whom use or authorize their use. They are few and far between, for good reason.
The caliber is likely fun as hell to fire, or so I've heard; however, for the LE\Mil lifestyle, there is little\no room for such hopeful idealism that it will live up to its hype. Hence, we stick with the proven products