In Trioplan images[1], the light intensity smoothly increases towards the edge of the disk of confusion, and creates a sharp edge. I agree that this looks kind of nice, although it's a quite specialized effect.
In mirror lens images[2], the "disk" of confusion is actually a ring, with two sharp edges rather than just one. This is not at all pretty, and as far as I know basically nobody buys these lenses for this effect.
This actually matters a lot, because other than this, mirrors are superior to refractive glass lenses in almost every way (note that astronomical telescopes are always mirror-based), so if it was not for the bad bokeh we'd all use them.
[1] https://fujilove.com/the-legend-and-the-bubble-bokeh-review-... [2] https://hoaiphai.wordpress.com/2011/10/18/recumbent-review-t...