Perhaps the change from re breather to CA-EBS / STASS?
Discussef in thread

Depends on the mission: how far out, water temp, kind of helicopter, mission. I wear a light, comfortable, horse-collar inflatable these days, offshore we were burdened with every idiotic gewgaw pressed on us by corporate-climbing safety managers. I trained HUEBA, but didn’t fly the water temps or mission profile to justify carrying it.