Mintex pads and discs are high quality items, something doesn't add up there, were the discs worn/scored on the BMW or were the pads a fast road as against a standard replacement item.

It's been my experience that the two makes you mention are first class products, often used by makers of quality cars for OE, look inside a brand new RR's discs you will find Ferodo pads nestling there.

Lots of other good makes too, every bit as good as OE, often same make as OE (Textar fitted to MB and BMW for example) and considerably cheaper from the good suppliers.

I wouldn't buy cheap tat from just anywhere though, and that goes for anything really not just brakes.

There is no possibility your mates 'Mintex' were counterfeit pads? There are such things and not always obvious from their appearance.