Twenty Percent Solution (Questions Must Be Asked)

A small mystery.

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Letter received with handwritten addresses.
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Sent from New York.
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Looked up the address. Non-descript building near former home of the New York Times. Many offices, including a few delivery boxes.

The faces in the flyer attached are unfamiliar.
Flyer

Faces Tipper

Their Web site elucidates the issue no further.

Is this the world's strangest, slowest, most-expensive word-of-mouth campaign?