Why would you need a wallet made of stainless steel? Well, you've probably seen ads for credit cards that allow you to just touch them against a sensor to pay for things. You might even have one! And, well, those cards are pretty vulnerable to being compromised by hackers.
Those cards have RFID tags inside, which allow anyone with an RFID scanner within a few feet to slurp up all their information. Not good! So this wallet, made of RFID-blocking stainless steel, keeps your cards nice and safe from anyone holding a scanner at butt level when you're walking around with your wallet in your back pocket.
How comfortable is sitting on a steel wallet all day? I'm not sure, but probably more comfortable than having your credit card stolen without it ever leaving your wallet.