Just a note regarding anti-squeal compound as used on motorcycle (and car) disc brakes.
Brake squeal is caused by high frequency vibration of the pad when applied. A little grease may damp that down but the risk is that when heated normal grease will exude oil (it is designed to do that) and lubricarte the disc itself - a bad idea!
Copper greases are
not anti-squeal greases. Copaslip and the other copper greases are anti-seize products for where heat will ldry away normal grease. E.G. exhaust bolts. The only use of Copaslip on motor-vehicle disk brakes is traces on sliding metal parts as the intense heat will dry out ordinary grease. Bicycle discs are never ever working that hard so I would not advise it!
Anti-squeal compound (also called "rubber grease") is a stiff and rubbery grease you apply to the rear of the brake pad where it contacts the operating piston. Usually it damps out the vibration enough to get rid of audible squeal. But some brakes do just squeak and it is hard to control
IMHO there is ablsoutely no reason not to use anti-squeal compound on bicycle disc components.
You can get it from most good bike or car parts shops in very expensive 500ml tubs or little sachets at about 60pence in UK
Jon