I've never tried a carbide expander ball, but I don't think they will help that much with concentricity, which is their biggest issue. It may or may not help with more consistent headspace.
There's more than one way to skin a cat. My preferred method for rifles is a body die followed by a Lee neck sizer. You can make a body die by lapping or drilling the neck portion of a normal expander ball die out, then replace the expander ball mandrel with a straight decapping pin. If on a single stage, you don't even need a decapping pin, as the neck sizer also has a decapping pin. Using two dies like this is both cheap, and gives you incredibly consistent brass. The best thing about the Lee collet neck sizer is you can use any size mandrel. You can make, or even order custom sizes. That is a much better method than using an M die, or NOE plug. I would even argue a collet neck sizer should produce more consistent neck tension than a bushing die, although if you are turning necks, it likely doesn't matter.