Interesting, I just made my own version using 2.5mm bearings as they looked like a decent size. I’ve found them quite nice in my opinion, and haven’t had the issue of dust on the contact point yet. It definitely has a bit of a “scratchy” sound but I had assumed that was from the texture on the delrin ball and not the bearing itself.
Since I also ordered 1.5mm bearings at the same time I’ll have to print another model that takes them instead and see if it matches your experience of the 1.5mm being smoother.