I picked up a SCAR17S yesterday. I own competing brands of 762 and 556 rifles, my user name will assist you in determining at least one of them.
I have not shot the rifle yet, just tore it apart to clean it up after purchasing NIB.
Here are my observations:
Most of these criticisms are based on it being the better part of 3 grand and directly comparing it to other rifles.
Positives:
Very light and feels well balanced
Stock is capable of folding and locking in place
Comes with Iron sights that actually function and fold
Piston operated so it should stay pretty clean
Pretty much fully ambi
Adjustable cheek weld on stock
Comes with a 20 round magazine
7.62 mm
Negatives:
You have to run a cleaning rod through the receiver to get the gas piston out
Gas piston isn't completely chromed
Reciprocating charging handle
Grip is absolute bottom drawer AR15 LPK
Safety selctor is poorly placed and smallish making it hard to operate
Polymer feels "cheap" -Completely subjective
Parts finishes aren't all a consistent color or hue
The stock feels especially cheap and I predict the lock will break
For the money they could give you more than a cheap-ass cardboard box
Trigger is not great, but I can make any trigger work. - Compared to HK MR series it sucks real bad
Magazines are proprietary, I don't care as long as they work
Magazines are expensive, I also don't care as long as they work
The level of build quality is not even close to that of the HK MR series
With all of that said I will shoot and keep the rifle as I like all sorts of rifles and this one is different enough to permanently enjoy a spot in one of my safes.
Sorry, I can't speak to the ACR........yet.