That's the one I just linked, and it broke, like really fast. I didn't even use it that much and the plastic tabs in the corners all snapped off.TNP New 3DS XL Case (Silver) - Plastic + Aluminium Full Body Protective Snap-on Hard Shell Skin Case Cover for New Nintendo 3DS LL XL 2015
I would love to see someone machine a metal replacement shell for these systems with a coat of the non-conductive "paint" they put on circuit boards on the inside of the shell. It'd be a bit of work moving all the guts from the plastic shell to the metal one, but it'd be pretty cool and hard to break. Add a silicone rubber protective skin to it and you'd have a virtual "military grade" 3DS.