From my past experience with them, the studies are usually testing 1-3 types of the same product, and you answer a questionnaire after (sometimes there's multiple questionnaires). Sometimes they require that you send the product(s) back, sometimes they let you keep them. And they don't tell you what the products actually are, or if they even make it to market so it can be frustrating if you fall in love with something. The questions always vary. The compensation tends to vary as well, I did one longer study where I got close to $200 in high end and drugstore products, and I've done normal studies where the compensation is just one or two drugstore items. It's always fun to do the studies and see what goodies will arrive though.