I have a DS lower and a J&T upper (J&T is the same company; they just use different branding for parts and accessories vs. complete rifles). I had to buy it in parts in order to meet the letter of some California laws, but in the end, I have a DoubleStar rifle.
Quality is great. The upper is a good deal nicer inside (polished, no tool marks) than the other upper I bought from someone else.