This universal app can be downloaded for free until February 20th exclusively by users of the Apple Store app. To get the free app, go to the featured page and scroll down to the offer near the bottom of the page. Tap on the offer and tap the download button on the next page.
Remember, the app is free only through the offer in the Apple Store app. If you go directly to the AppStore, you will have to pay for the app.
Edit: the free offer is apparently only available to those iPad users with access to the iPhone version of the Apple Store app.