I posted a picture of them in the other thread about these. They come on a strip spaced 0.1" apart. Ours don’t have a top strip, but many do, for even better alignment. If you push a strip of leads onto the edge of PCB, they clamp on and maintain alignment until you solder them. So production work does require a jig, but you would not have difficulty doing these by hand.
Through-hole pins depend on solder fillets for axial strength, edge pins are mechanically reinforced with tabs. Therefore a through-hole pin requires a solder pad to extend out beyond the centerline of the pin, increasing the required width of .6" pitch DIP-compatible PCB to at least .7" or .8". A 25% increase in PCB area is significant over large production runs. I would not trust a square header pin soldered into a half-round castellation, all axial forces are now translated into twisting forces on the copper adhesive and the un-reinforced solder fillet which is only wetting one side of the pin.
So I think the edge clip pins do have some immediate advantages if you’ve committed to this type of design. But for occasional hobbyist use, it may not have enough of an advantage to justify the effort in locating a source, when normal 0.1" headers are so widespread.