unlike Alexa, increased traffic does not mean much on Google rank. rather it can cause penalties by Google search engine, especially if it comes from an automated bot traffic aggregator. I'm not just thinking about your service here, so it is with all purchased traffics. more risk than benefit.
Google itself has repeatedly emphasized this, the amount of traffic does not bring or brings very small website rank improvements.
btw. how long each "visitor" stays on the website?