You don't have to buy it after the "trial" period is over, although the version of Deep Exploration that comes with the free version is a real time limited demo so after the trial period, you lose the extra file import options that DE provides unless you buy or already own a DE license. The free version of Enliven will keep working and will correctly sign Viewpoint content even after the "trial" period is over. Enliven does embed IE, sort of like Poser does. However, in Enliven, the purpose of the embedded browser is actually to preview the content you've created using the real browser and VMP plugin, before hitting the "Publish" button. The content created in Enliven should run in quite a few browsers, and work on Mac and PC.