I have observed the notch less sights on percussion rifles before.
Such sights have yielded very good results with my aging eyes on my own rifles. I can't see the platinum line, so don't bother with it.
They seem to work like an aperture sight, where one's eye naturally centers the bead on the leaf.
A bead somewhat larger than normal is a big help. The size is not a problem blocking the target, as the bullets strike at the top of the bead.