The first mate last break connector is suitable for many applications as many alternative energy applications and others need to ensure they are grounded when they first plug in the connector.
By making one pin slightly longer than the others, it will always be the first to mate or make contact and when demating it will always be the last to be in contact as the plug and socket separate.
The first version of the Mil-E-Qual connector also has UV inhibitors in the plastic.
Manufacturer Conxall also offers this grounding pin feature on some of its other connector ranges.