There is concern that the use of one of these units with a bunch of keys or whatever hanging from it, with that added weight, will deform the vehicle side socket or break the socket from the board to which it is attached. USB A connectors are pretty robust, but the sockets aren't indestructible, and with everything being SMT these days, a lot more sockets are being peeled off of boards.
This problem can be exacerbated by weight on one of the units that "slides out" with a thumb slide. In the event that it's still half retracted when you insert it (you wouldn't get a connection, but it could still be inserted 1/2 way), the lever created creates even more force on socket.
As for metal - I have yet to see a thumb drive that didn't have a metal shell around the connection. It's part of the USB standard. I don't see any specific mention of that in the bit of art you clipped for us.