I use Kool Stop Thinline (salmon) shoes on my commuter with Weinmann 610/750s. They, the Supra model, and maybe some others have radiused cup/cone that allows the shoe to be rotated to get toe-in and also to align them vertically, so that they contact the rim surface squarely. I like this feature a lot, though I've bent arms before, even on a pair of Campy Super Record calipers -- that works too. Even adjusted with toe-in, I've found that the Kool Stop shoes will squeal for awhile, until they're worn in a little and seated. This may be a function of their "grippiness," as noted by dddd above. And even when broken in, they'll squeal on a really humid morning, or right after I've cleaned the rim braking surfaces with isopropyl alcohol.