I have done around 10 of these free new offers(install app and run) and have not received platinum for them. I am an avid user of tapjoy and have never had any problems with them. However, this w3i company is seedy and unreliable. I have finished around 10 of their offers, and for the last 8 or so have not received any credit, despite w3i directly reporting that these offers have indeed been verified in the history tab - new offers. From this, I can only assume that the company offering the platinum, w3i is a scam and a fraud, and firmly suggest STS disband from any affiliation with them.
Thread of other people attesting that W3I indeed does not accredit their offers.