Doesn't seem any have much to say about Ares, and my experience is limited but I'll offer what I know.
I bought their NiB BCG when they had it on sale awhile back and have been happy with it so far. I was a little leary of it at first because of the investment cast extractor and gas key, and there may well be a durability issue later, but up to this point I have about 300 rounds through the rifle with 0 problems. It extracts, chambers, and the bolt locks up perfectly, Extracted casings all land in about an 18" circle about 6 feet to the right and about a foot rearward of the ejection port. Based on the specs for the Harpe upper, I suspect this is the exact same BCG as I have but Phosphated rather than NiB.
Ordering and shipping were fine. I think it arrived 4 days after I ordered.
Depending on what you intend the rifle for, or budget constraints, I think the Ares BCG is just fine. (I think its the same BCG that Aim Surplus offers) If its a recreational rifle, plinking, or paper puncher its great for the money since an extractor, gas key or general BCG failure will only result in having to pack up early and buy a couple replacement parts.
If its a duty rifle, or self / home defense rifle, then pay the extra hundred for the Bravo Company or DD unit. It will be the cheapest hundred ever spent compared to a failure when lives are on the line.
I can't speak to the Harpe barrel, its probably decent, but you get what you pay for.
The whole battle with the San Diego BATFE makes me a little nervous. I understand where Ares is coming from and I think they are right, and BATFE has overstepped badly. However, I fear that Ares Armor is making everything a little too public and shouting a little too loudly, and that the fight is going to make someone in DC take another look at 80% lowers and close that door altogether. I'm not wild about BATFE having taken the customer list from Ares since my name could very well be on it, but then I guess there was a record somewhere and obviously the govenment can seize it anytime, anywhere regardless of the law.
About all I have to offer on the subject.
hope it helps.