Why would users ever want to volunteer their time to do these surveys? Because in return for filling out surveys, the survey companies pay users a small remuneration fee.
Survey Junkie is a market research company that provides other businesses with opinions on their products/services. Apple comes out with new products, and they want a genuine opinion on them. They would hire Survey Junkie to help them out.
When you complete surveys, you can earn anywhere from 20 points (20 cents) to 350 points ($3.50). One survey may take an estimated time of as short as 2 minutes or as long as 30 minutes to complete.
Survey Junkie IS a legitimate way for you to make some money. It has a platform with over 6 million members that offers an excellent way for businesses to do product testing and collect information (in exchange for some money).