Several years ago, there were no metal casings. The luggage tags were very fragile. I never put my MPC tag on my checked luggage. That became my habit. I am still not putting my MPC tags on my checked luggage.
I do put my MPC tags on my cabin bags, but I am using my old tags most of the time because I like to have my GR, SL, GO and DM tags all on, and I cannot do that with the metal casings.