There are, as far as I've been able to determine, two distinct differences between "cheap" pads and "expensive" pads.
First, the way the pad material is mounted to the backing plate.........either glued or riveted. The more "expensive" pads are riveted, but I think it's more to do with the car manufacturer's preference.
Second, the pad material. True, cheaper pads use softer material vs. the more expensive ones, but this in itself is not any cause for alarm. True, softer pads will wear out faster than harder pads, but harder pads wear rotors faster, take more heating to become effective (which is why I chuckle at persons spending lots for carbon based pads.....carbon pads need so much heat to become effective stoppers that on the street they are a tad ineffecitve for that sudden out-of-theblue panic stop---racers use them but in racing one is on the brakes much more often vs. street use), and harder pads can squeal more than softer pads.
Cheaper pads, ie. softer pads, won't damage your rotors.
Squealing can come from several reasons........glazed pads (they became overheated and developed a glaze), worn pads, or anti-squeal prep on the pads when installed wasn't used.