All demos are candy coated, at most you will never be able to get the product to sound how the demo sounds.
The synchron Strings may or may not sound better that VSLs existing string librarys as sound is very subjective.
One advantage is you will get the recording of the Syncron Hall, second is if you go for the standared version you get a complete set of articulations, 3rd there is a player that is being built for the syncron serias that offers plus possibilitys.
That alone is worth the pre order with out any demo, if you have the cash wait until its releast and see what others say about it, then you can make up your mind.
Very weird logic. (I did preorder by the way)