Hey there!
To answer your question in short: Both. It's a premium for the name, but it's also a quality product. It's the fact it's proprietary that makes it a bit different. It looks like an AR and basically is an AR, but most of the action has been changed. It's sort of apples and oranges.
There are people that buy SR's and then fill in the receiver and have it recut to say "M110" and then they'll proceed to replace the URX4 tube, barrel, stock and other parts and once they have $10,000 in it they'll have a reasonable facsimile of an M110 (then they find out they could have called KAC and bought an M110 with deployment kit for the same price!).
No way I'd build one to copy it, but a new rifle? Yeah, it's one of my favorites. But guys on here have REPR's, GAP's, Larue, etc., as well as custom and/or upgraded this or that. They all shoot under 1 MOA and all cost a similar price, some may even be as reliable. When you consider that and the fact it's a proprietary rifle, then it either makes it worth more or less, depending on how you view the proprietary parts. And you can build a lot of rifle for $4000.
But attention to detail, quality, it's all there. Barrel is cut rifled, brake REALLY works if you have one, suppressor is probably the "best all around" I've used or have (true QD and self indexing) trigger group is on par with Geissele, BCG is reliable, the lower is ambi and made that way, not an afterthought. The flip sights are IMO the best out there. There is no junk on the rifle and nothing was overlooked. The LMT stock on a 20" rifle may seem odd but it grows on you and is actually a pretty smart idea. URX 4 essentially turns the upper into a monolithic, more or less.
Here's some KAC porn for the meantime. USO 3.2-17x behind a KAC PVS 30, Atlas bipod.
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