It's not worth your time, all they offer are silly gifts lime:

Usually, we offer a variety of gifts to thank you for taking part in our surveys. These range from flashlights, laser pointers, Blockbuster gift cards, pocket knives, Barnes & Noble gift certificates, Starbucks coffee, Inova brilliant keychain microlights, jelly beans, or crisp new 5 Euro banknotes

Sounds like things you can buy at the 5 and 10 cent store.