My mountain bike uses that same under-the-chainstay U-brake system, and it works extremely well with KoolStop pads. (My front brake is a SunTour RollerCam, which requires the same above-the-rim mounting bosses, which are incompatible with standard cantilevers or V-brakes.) U-brakes and RollerCams may be evolutionary dead ends, but they are definitely not deal-breakers, in my opinion.
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"Far and away the best prize that life offers is the chance to work hard at work worth doing." --Theodore Roosevelt
Capo: 1959 Modell Campagnolo, S/N 40324; 1960 Sieger (2), S/N 42624, 42597
Carlton: 1962 Franco Suisse, S/N K7911
Peugeot: 1970 UO-8, S/N 0010468
Bianchi: 1982 Campione d'Italia, S/N 1.M9914
Schwinn: 1988 Project KOM-10, S/N F804069