The surveys are, in my estimation, a clever scam. Nothing more.
They can (and, I believe, in many cases do) ask you the survey questions under the guise of "qualifying questions", then, after they have your information, tell you: "sorry, you didn't qualify". They get the information they want (and are getting paid for), you get nothing. Rinse and repeat. You can't dispute it, because "you didn't qualify" is pretty subjective, and you can't prove that you DID qualify, can you?
To date, I've taken over 100 surveys, and in every case but one, the above (or a slight variation thereof) has occurred. On exactly ONE occasion I actually got the reward at the end of a survey. Good luck to you.
Offers are a different story; with screen shots you can "prove" when you've done your part to fulfill an offer; as with surveys, they often don't initially pay you the credits you've earned, but unlike with surveys, I've always been successful in using screen shots to procure the credits I have rightfully earned. Nowadays, I stick to offers and skip the surveys.