I've never heard of Vindale Research and I only do surveys for Pine Cone Research. There was a comment by a member 2/2009 about liking Opinion Outpost [www.mysteryshopforum.com]
I have never found a Vindale Survey which did not ask me to first purchase something. Since I do not want to make purchases in order to complete their surveys, I have opted out of their e-mails.
I signed up with both a couple of years ago and don't like them, stopped messing with them. They want you to buy things..... I just want money ..........LOL
Opinion Outpost is one of the best survey companies, surveys usually pay at least two dollars for less than 15 minutes and topics are interesting. They always pay quickly too.