The Tektro pads on my bikes have those bits of metal in them too. They were literally destroying my rims and so I got rid of them off one bike and will soon do so on the other bike. Koolstop pads seem to be the best way to go. For one thing they are consistent and you know what you're getting. Also when you hit the picks, you do not hear that scraping sound letting know your rims are being torn to pieces.