Avoid them like the plague. In theory, kickstarter and indiegogo seem like a great idea but if you think about what is actually transpiring, you're better off creating your own website for your particular project.

The premise is that you make a contribution to the company so that they can finance commercializing their product for which they give you one or more of the products they are trying to commercialize. What you get back for your contribution is based upon the schedule that appears in their Kickstarter presentation. As Yvette mentions, your contribution is just that; it's at risk that the product is finalized and made commercially viable. Most of the projects I've backed in the past have come in way, way late and after a lot of fits and starts. And, Kickstarter does not help. In fact, my experience has been that they are pro the developers and don't (won't) step in to help if the developers can't deliver. Buyer beware.