Yes, this is a genuine product. The company is called Garment Guard, and their products include Garment Guard perspiration protection for your clothes. Their newest product: Subtle Butt.
Each 3.25" square filter has two layers: one made of soft fabric with an antimicrobial treatment, on the side touching the skin. The second layer is activated carbon, which faces the underwear or the pants (for those who go "commando") and has a "vast surface area" for odors to adhere to and get "neutralized." Two adhesive strips hold the Subtle Butt in place.
The price: a mere $9.95 for five pads and peace of mind. Though a "silencer" feature would be a good add-on.
To be honest, I remember seeing a joke commercial on Nickelodeon where they suggested putting a dryer sheet in your pants in case of gas; maybe this company stole / improved on that idea.
BTW, here's a link in case you have a gassy friend you want to email this to.