Keep in mind that many of your potential customers will see that it's Mac-only and just move on. Windows is still by far the market leader, and you're really limiting your potential market by not having Windows support.

That being said, this seems like the type of product that Mac users would be more likely to go for, so you could just hold off on a Windows version until you know whether the product is viable (based on sales)

One more thing: The "buy" button is not obviously for that purpose, and I was about to comment asking whether you can only buy from within the demo. Consider rewording the button to make it clear that that's where you buy the product from.