I have a DS STAR-15 lower with a Stag LPK I put in it and a complete 20" A4 HBAR upper from J&T (Same company as DoubleStar, but it's the side that sells parts, uppers, kits, etc.). Fit, finish are excellent. Reliability excellent so far. Accuracy, too. I'm quite happy with it.
The Stag LPK was what I happened to have; I acquired this stuff when the AR first reappeared in California, and at that point you took what you could get. I'm sure the DS parts are the same.
Essentially, I have a complete DS; for California legal reasons, I had to put start by buying a stripped lower, not a complete rifle.