My only requirements included light weight, twist rate, the back-up iron sights, NV capable optics and suppressor.
Sully spec'd the bulk of it with input from Pat Rogers and Denny Hansen.
I consider it a General Purpose Defense rifle. Were I in Harm's Way, I'd consider it a pretty damned capable battle carbine. I honestly can't think of anything I'd change on the rifle.
I'll argue guys like Pat and Denny to my grave that iron sights are all round better for defense or offense than the Aimpoint. They both appropriately point out that the Aimpoint is really helpful in shooting on the move. I grant that, but it's also real UN-helpful when the sun is coming up or going down or when we're moving from indoors to outdoors or vice versa. The dot NEVER seems to be at optimum intensity when you really need it.
Personally, I believe Aimpoints and Eotechs are great sights if your goal is to teach someone, in compressed time, to be a mediocre shooter. OTOH, my Grail sports PVS-14 Night Vision and that would be pretty damned useless without the optics. So, I really haven't much room to bitch.
The overall workmanship and dependability of the rifle has made it my go-to carbine. But I'm not certain any of us can quantify this type of thing. We trust what works well for us. The trigger is as good as a field piece might be. Accuracy of the piece for field shooting is a non-issue. The Crye MultiCam coating is a cool conversation piece, though expect it to weather with use.
Sully talked me out of the standard surefire combat light, in favor of their Scout light. It was a good call.
I swear by the Sully stocks (in their shortest possible configuration) and the QD, "tactical" loop sling is the first one I've ever used that's imminently functional without making me feel like a "warrior wannabe" when I clip into it.
Obviously, I'd not think twice about recommending the Grail for defense, class or battle.
Hope that helps-