My experience with smooth post Kool Stops is different. I've used the black and salmon, both ended up squealing., but the do work nonetheless. Yes, I know how to set up canti's..... as I have for decades. When I replace the Kool Stops with original vintage Suntour and Shimano pads, no more squeal. It's frustrating, but the truth is the truth.

Velo Orange's Squeal Free pads and holders may be better .... I don't know.