They can most definitely scratch hardware that is on the bags, you need to be extra careful. That's probably why I don't do bag charms, but they make great eye candy !!
not majoryly, but if you use it alot of are rough with it, it will cause minor scratching..no big deal though i use my pastilles all the time and its fine..
I love the look of the bag charms....was very tempted to purchase one when I received my Montgorueil PM last week.....But I keep my $ for the bags...not the charms!!