Good read on this rifle.
http://www.gunsandammomag.com/
[ol]
[li] Can anyone tell me what is wrong with the ergonomics of that light? 
[/li][li] The article says the spent casings were hitting someone two benches down from the rifle. Those benches must have been downrange, because – unless something has changed – the 556 has the same ejection pattern of the original Swiss 550-series rifles. Spent cases are ejected so that they strike an angled part of the upper receiver and bounce (quite forcefully indeed) forward at about a 40-degree angle.
[/li][/ol]
Sympathetic reflex grip causing ND’s?
Well, a Magpul CTR as standard is sure a step in the right direction.
Bingo. First time I saw that a year ago, my reaction was a hearty “WTF?”
Huge +1 on that.
Complete Disaster
I looked at one of these yesterday … price was $1300. My friend explained to me how completely different the weapons system is to an AR. If it was full auto I might have looked more closely 
While I worked there, I had “SWAT” guys from ICE, FBI, DS, FAMS, USSS, as well as SEALs and USASOC operators all voice their opinion on that light and the trigger-style activation problem. When it went forward regardless of these warnings, I actually took the time to write a CYA letter to the company’s General Counsel explaining in detail what “sympathetic muscle response” was and how it could lead to a serious oopsie with the light.
I’d like an actual US made 551 with the original stock design or the original slightly modified to be LOP adjusting if that’s not too hard for them, but the 556 regardless of putting a B&T style railed forend on it and CTR on the back is still nothing more than taking a great design and trying to make it an AR instead of putting a bit more original thought into improving on it.
The operating system is nice, but I’d rather just have more POF piston AR’s than a 556 anyday and have another great operating system and alot of parts commonality and pluses besides.
If SIG had just made the steel lower they wouldn’t have had any finish mismatch to begin with and could have salt bath nitrided the whole thing and made alot more people customers. The weight savings is meaningless to me for so little savings, but more importantly that it throws the balance off like it does and looses some strength and style in the design besides. For those individuals that can’t handle the weight of a 551 even though there still a light rifle, there are certainly enough superlight AR’s to go around.
Weight was a major design issue in bringing the 556 to life. As someone who sold the 551/552 to military and LE customers for five years, I can tell you without question that the weight of those guns compared to comparable-size M4 variants was a significant deciding factor for many people. When the first prototypes came out, many of us still complained it was too heavy. Slightly mismatched shades of black between the upper and lower aren’t nearly as important to most people as functionality.
The styling (which is all the stock and forearm really are) was also very purposely intended to attract people from the huge AR market instead of trying to create a separate new “550 market” in the U.S. While folks at M4carbine.net might be familiar with the 550/551/552, the gun-buying public as a whole and even more LE/mil folks have never heard of the things.
Now I see what you’re talking about - yikes!