What's in it for you? Up to $25 in gift cards. Our panel management partner, Knowledge Networks, will give you a $5 Amazon.com Gift Card code instantly when you sign up and download the Google Screenwise browser extension.1 Then you’ll get additional $5 Amazon.com Gift Card codes every three months for staying with it.2 It's our way of saying "Thank you."
Google

Do you think 20$/mo it is cheap?

it is remind me this case:

Zuck: I have over 4,000 emails, pictures, addresses, SNS
[Redacted Friend's Name]: What? How’d you manage that one?
Zuck: People just submitted it.
Zuck: I don’t know why.
Zuck: They „trust me”
Zuck: Dumb fucks.
Well, These New Zuckerberg IMs Won't Help Facebook's Privacy Problems - Business Insider