I've used Rockey Brass several times with great results. The Poly90 frames are built by Poly80, so they are pretty much the same everywhere. The bigger issue may be who makes the upper and lower parts kits. The ones from China are cheaper . . . for a reason. Several companies make slides and barrels. I would suggest limiting the number of different providers because while they may all claim to be OEM spec, you may get parts from one place on the small side of the spec, and other parts from a different company on the large side, and suddenly you find they don't really fit and work well. If a reputable distributor has put together a 'completion' kit, I would think they may have taken steps to ensure they are most likely to fit together and function correctly.