I have one, and I love it for killing game up to about 300 pounds. I and several of my friends have hunted with our 6.8s for the last 3 seasons, and we are up to 36 antelope and deer taken so far.
It's just what you'd expect. It's almost a ballistic match in velocity and bullet weight, to the old original 257 Roberts shell.

257 = 117 gr. bullet at 2620 FPS ---------- 22" barrel
6.8 SPC = 115 gr. bullet at 2650 FPS -------16" barrel

I know that a few units of the US Army, Navy SEALS, and USMC Hunter/Killer teams have them, but I don't think the US military will go to it across the board. THEY SHOULD, but the accountants have more "sway" in such things than the troops in the field, and always have.