You might want to ask the same questions on the AR-10 and AR-180 forum. There's bound to be more folks with knowledge about the gun there.
I bought one two weeks ago. I like it, it handles nice. I used to own a pre-ban Sterling and it's mostly an improvment. The plastic lower has alloy walls that the pins go through for the internals, so it's not like the plastic is going to wear out from shooting it. It feels as good as the original ergonomically, except the stock feels even better. It doesn't fold, but it's a stronger stock and more comfortable. It's not molded as one piece with the receiver, but is a separate item, so it's replaceable.
Armalite designed it so that you could remove the built-in brake and replace it with a Flash suppressor, so I doubt that it would have an effect. Same with the stock. They supposedly have a folder designed for it, just waiting for the AWB to sunset. I'd check with Armalite to find out the real deal before hacking anything though.
There's only a couple things I don't like. The selector doesn't have any "clicks" to it. It just rotates. The pistol grip is a little too slick, but I'm going to shoot it first before trying skateboard tape. The hanguards don't have heatshields. Maybe it's not important, I won't know until I shoot it. Looking at the hanguards, it would be easy to put some in if they need it.
I'm not in to hanging 12lbs of gizmos from my rifle, so I don't mind the original scope mount. It does what you need. Others would sensibly like rails everywhere so they can put their stuff on. Some folks don't like the lack of a chrome bore. I'm not too worried about that either, but I would rither have it as well.
I think it really handles nice, and it very light. When I can put a folder on it, it will be better than an AR-15 IMO. Of course I used to like the original AR-180 better than the AR-15 to begin with.
There's not much to dislike, and a whole lot to like about the rifle.
Ross