The new design incorporates a lock that accommodates the different lengths of wire used with a single contact point thereby ensuring it works consistently and safely.  The brass screw and plate of the switches are also rust-free resulting in durability and better performance.

The twin hole contact point is a problem as the different lengths of wire tend to slip and prevent good contact taking place.  It has also been known to spark leading to bigger problems.  Furthermore, the steel screw and plate gets corroded easily, especially in moist conditions, and affects the performance of the switch in the long run.