I started off with the Redding bushing die and was banging my head against the wall with the runout I was seeing. I even tried resizing the necks in two steps, and it helped out some, but runout was only about 50% better from ugly. I finally got a Lee Collet die and runout, if any, is negligible and easily corrected on my Hornady concentricity tool.
I am still on a factory barrel, and there is plenty of neck diameter clearance in its chamber - approx .008". I am wondering if the bushing neck sizers do their magic with custom barrels/chambers that have closer tolerance neck diameters. That way, the brass doesn't have to have near the amount of resizing done to it like factory barrel/chambers would require.
One thing I learned to do with my Lee Collet die, is to wipe a little case lube on the tapered section of the fingers where they go up into the mating top cap about every 100 neck resizings. I unknowingly ruined my first collet die from lack of lube on top of those fingers. If this upper section of the die doesn't work properly, you will mess up some case necks.