I have one of these, and after a mystifying experience at airport security, I discovered that the RFID shielding is made of metal. No clue whether it actually works, though.
"REAL ID Act and RFID: Privacy and Legal Implications," a talk at The Last HOPE, tested one such wallet, and determined that while it's closed, it works--but the one they tried sprung open about an inch when placed on a table, and the rfid card inside was still readable that way.
I have a passport case and a wallet from DIFRWear. I don't carry my passport everyday, but my public transportation card works with RFID and it's definitely not working when kept inside the wallet. Surely it could be read when I'm actually using it to get in the station, but once in my pocket there's no way to copy or read it.
I haven't had the occasion to try the shielding of the passport case either.
