Having owned several Flex's that have had the pivot forward of the Crank/BB and seat post and where the later ones sit rearwards of the Crank/BB. As to the benefits i'm not sure and in all honesty both set-ups have slightly different riding characteristics but as to pros and cons over either design i could really comment as i enjoyed riding both. I also own an Orange X1 and it does have a URT (Unified rear Triangle) where the Crank is fixed within the URT and the whole unit pivots independantly. Again the X1 rides different to the Flex's, the X1 doesnt bounce as much as the Flex's and when applying drive rear wheel traction seems improved. One of the most significant differences i have seen is with the removal of Elastomers and fitment of Noleen or Risse shock units, once set up the ride of a Proflex is improved greatly.
Good luck with the search for your next Flex
"Would anyone else rather be doing something other than marching up and down the square????"