That's one way. Certainly quickest.
I just started doing the surveys a week or so ago. In that time I've collected over 2500 credits. Just doing the ones listed in the little blue lines, i.e. the ones that do the pre-qualification. With some, you don't get anything. Others, you get 5 credits for trying, and then you get the surveys that accept you and take you all the way through.
I don't mess with anything that wants my phone number or address. I set up a second email account in case a survey wants an email address, but the ones I've been doing have never asked for one.