The Izumi V half-link is an expensive NJS part that uses a screw and nut instead of a press-pin to attach the link to the chain. It is really overkill for normal road use, and a much cheaper press-pin half-link will work fine. It is convenient when removing the chain for cleaning or any other reasons. The only reason I use one is that it came with the Izumi ESH chain I use on my track race bike.