Here's a bit more info. from the site:
This page explains in very clear terms what they "get" out of this:
"What does NWPS get out of the program?
The bonus code we’ll give you corresponds with an affiliate account we have with your poker site of choice. In return for sending a new player to their site, we receive a small portion of the rake they generate. However, due to the affiliate payment structure, it’s difficult for us to make money with losing players on our affiliate account."
All of their bonus code stuff is on
this page.