The big difference between Premium and Pro version is that If you buy Premium script, you will get source code. While on Pro script, you won't get source code.
Another common difference is that if you buy Pro script, We will provide shared server hosting for your domain. We will provide hosting until your purchase license exist. If you want to host site on your own server, you have to purchase Premium script.
To see more difference between Premium and Pro version, You can click on "Pricing" or "Details" button on Products page.