The advantage of the armlock is multifaceted but the main benefit is increased face control. We orientate our JMX/SIK grip parallel to the putter face for maximum contact points, ensuring a stable and square setup from address through impact.
If the L.A. GOLF SHAFT is an option for you the benefits in face-angle consistency are measurable. The shaft is extra-stiff but is also very responsive and retains a "buttery feel" on center strikes.