I am with about ten different companies and some are far better than others, some send you a cheque when you reach a target. Others you can redeem for high street vouchers. There are also some that let you test products and pay for your opinion is a pin money earner, though one I use is to scan your shopping when you get home and that has earned me quite a bit over the years,
You do of course have to reveal a lot of details about yourself, so be sure they are trustworthy companies.