Reason 1: Ergonomic extra thin wallets are better for your hips and spine, guys.
Do you keep your wallet in your back pocket ever? Did you know that a fat wallet in your back pocket can cause sciatica and hip displacement?
Reason 2: The extra thin, non-leather nylon material used in the construction of most of their wallets.
Most of their products are non-leather but they also produce some leather wallets. The leather wallets are very clearly labeled, though. So that's helpful.
"RFID" stands for "radio-frequency identification". In other words, the strips and chips on your cards. An RFID-blocking wallet creates a faraday cage around your cards to deflect the signal thus protecting your cards from being scanned by identity thieves.