Podium Racing is currently selling those Koyo. How were they? I had read that these aftermarket tapered were better than the OEM in terms of durability.
Complete BS.
Just like tire's release agent story, people are still talking about the old story from 70s and 80s.
(which means, those people are just repeating things they heard from someone. Not from their experience.)
Back in the 70s, 80s (and earlier), motorcycle's steering head bearings were
loose ball bearings.
Back then, switching to tapered roller bearing was popular upgrade, and it was rightly so.
From the end of 80s, toward mid 90s, manufactures used tapered rollers.
(First Monster (1993) had tapered roller, first R1 had tapered roller...)
Then, by the end of 90s, starting from top of the line sport bikes, they went to
caged ball bearings.Caged ball bearings are easier to install, easier to maintain steering head properly adjusted,
smoother, less friction, there's nothing wrong with them.
(loose ball bearings get sloppy when the races either loosen or wear. That's why switching to tapered roller was poplar,
in the 70s, and 80s.)
BTW,
NTN (Japanese bearing manufacturer, they are specialized in bearings and CV-joint) is Ducati's OEM supplier for steering head bearings.
Koyo seiki(is a part of JTEKT now) Aisin seiki, NSK, Borgwarner, are quality bearing manufacturers,
You can search thier PDF catalogue if you want.
You can even contact with theier customer service.
Those "kit" bearings are made by "unknown" company.