the correct name is "Casascius" and it is not offline storage, it is a physical bitcoin
I'd hardly call a gimmick silver coin with a sticker over a QR code a secure method of storage.
In any event, any of the coins that have been "slabbed" with the sticker still intact you would have no way of knowing whether or not the sticker was peeled off, the details transcribed and then carefully replaced immediately prior to encapsulation. (We'll know for certain one day into the future if someone decides to cash in the funds)
Actually, its pretty easy to know...simply check the firstbits balance...if it's still there, the coin is not tampered with. Any scammer would steal the balance asap.
Collectibles are gimmicks to some and treasures to others...market determines true value...