Ciao.
Is it normal to have small metallic pieces stuck within brake pads? How do they appear there? Is it from the rims and braking or did I get them from "the street"?
I believe that the pad has caught something tiny, sharp from "the road" and over time gathered chunks of alloy from your rim while braking.
"Carbon is faster"
That is fairly normal. As nikko stated, it's usually a result of some grit or debris on the rim becoming lodged in your pad, which then digs into the aluminum, collecting metal flakes. I always examine pads during tune ups to check for this. Your pads dont look too worn out, you could solve the issue by using a pick to remove the burrs from your pads, then filing or sanding them to remove any metallic buildup. I will also usually lightly clean the rims using some fine grit emory cloth to smooth out any burrs on the brake track. Sometimes new pads are needed, the rubber does harden with age or glaze over from heat making this issue more prevalent with cheaper or older pads.
I replaced brake pads last week on a couple of bikes and used Jagwire brake pads. Do you consider those as quality pads? Thanks