I used to run a Sailor Moon Fan Site. That has nothing to do with making money online or running a business, I know. However, I think I can offer some feedback on this because I used to try free traffic sites.
Does it work? Well, it DOES bring you traffic. You just have to spend hours earning credits so that your site appears. If you have a counter, the numbers will go up pretty fast depending on how much time you spend getting all the credits. This is were the downside comes in. You are getting traffic but that's about it.
Most of the time the people who are looking at your site are only looking at it in hopes of getting more credits. If you are lucky and you are trying to promote a unique free program, you may get a few sign ups. Even more so if most people are using the service to do the same thing. Which, can cause problems if everyone is trying to get sign ups for the same program. However, if you have your own business the goal is to get repeat visitors, not one time viewers who more than likely have no interest in what you have to offer. It is better to work on search engine optimization. So unless you are getting paid for the hits you receive or promoting free programs, the free traffics sites are useless and almost a complete waste of time.