The Neilson Disc Hub is aluminum, but the plates themselves are steel, and I can't recommend them enough. I had two aluminum discs that I returned/sold before going with the Neilson system. Just picked up a second hub.
I absolutely love the "modified" bevel edged flat discs for it. They're extremely handy for getting into tight spots.
My Neilson hub is super accurate, and I find the discs to be incredibly convenient. Fine paper wears out super fast, and you're constantly changing it, on the other hand, course paper usually lasts longer, and before using this setup, I was constantly ripping good course paper off, to put fine paper on.
I'll also go against the "popular opinion" and recommend flat discs, vs the tapered ones.