GMzH: The prologue is included in the main game, too. The only benefit could be the saved games - I'm not sure whether the main game would make use of the files from the prologue version or whether you have to start from the beginning in any case.

On the other hand, you can also start into free play directly if you played the prologue completely. There are some additional elements, especially according to factions, with own tutorials, but the basics are well known after the prologue.