Sin PvP weps

Actually, it's still quite useful to have an extending main hand, since you can kite glads/templars, also you can utilize your fang strike chain w/o moving (since with non-extending weapons you gotta move after the push-back effect appears) so yeah I'd say extendable is a great advantage in PvP, but only if you're willing to give up on that extra damage which you could gain from double ABG.