In the event that you are required to make a purchase, you will be reimbursed and you will get to keep the item. The main difference is that these programs pay cash. In other words, these programs are the same as reward programs but rather than giving you free products and gift certificates, they give you free money. These companies will give you free stocks or free shares in their organization. In other words, they cannot be bought or sold as of yet.
Some companies never do.
If you take advantage of these offers, you may have to wait years until reaping any benefit, and in some cases you never will. Even so, I recommend that you sign up anyway. After all, you have nothing to lose and if they do IPO, you have everything to gain. These aren't really free money offers. They are free product or service offers.