You would have to check with the manufacturer as to what protection they guarantee. If you buy a cheap RFID from a seller in China you will most likely be getting a good-looking fake that offers no protection at all. So find a seller with great feedback who only sells genuine items. It will cost more but when it comes to protection, no sense throwing your money away on a cheap look-alike.
Also, if you choose your sellers from North America (under Item Location, left side of page) the chances of the item arriving quickly, being genuine, and being exactly what was pictured in the listing are a lot better. A few links to skim if you want to think about which to buy:
http://www.makeuseof.com/tag/what-are-rfid-blocking-wallets-which-should-you-buy/
http://www.infoworld.com/article/3023422/security/why-you-dont-need-an-rfid-blocking-wallet.html
http://www.consumerreports.org/cro/magazine-archive/2011/june/money/credit-card-fraud/rfid-credit-ca...
