I've said elsewhere back when these were announced...
According to one comment on YouTube, the longer cut of the film is supposedly edited in the finale. Certain graphic deaths including the final fatality were cut to be a little less graphic. The shorter version of the film has these graphic deaths intact.
I've not really looked in to it since I read that comment so I can't comment on how accurate it is, but it kind of ties in with how the previous Rambo movie had a director's cut which was longer but chose to tone down the graphic deaths. As I said elsewhere, if this is true I think I'd prefer to own the shorter cut with the uncensored violence and have the alternate opening as part if a deleted scenes section.