The 840 release mechanism is an efficient and durable system. 

Reflex User Manual

The new 840 release mechanism is constructed with arms of stainless steel. The shape of the release arms have also been designed more vertically to keep the heel strongly connected to the plate.  The new 840 release is good for use in salt or brackish waters and for skiers who like to keep their rear foot big toe near of the heel of their front shell.

It features new additional tension settings.

Plus the release mechanism has added brighter bolder colors