I used the "old school" steel hook snaps for 30 some years and making the move over to using carabiners wasn't a smooth one for me. Mainly because of the way you have to grab to open them up.
I recall using Greg's gear once and the biners he used opened different ways. One biner was, pull-down, twist clockwise and squeeze to open and the other was pull-up, twist counterclockwise and squeeze to open. And ideally you like to have some tension on the biner when opening them. Loose biners are more difficult to open. Especially for a newbie. Well, it really got me frustrated and Greg looked up at me as ask if I was having trouble. It was easy to see that I was.
The thing about it that struck me the most was the fact that if it was an emergency or stressful situation and I had to make a quick clip in or out I would not have been able to do it.
Carabiners are so different that before sending any newbie aloft I always make sure they understand how the carabiner functions and try not to mix different ones on their saddle.
Heck I see groundmen spend a minute sometimes trying to figure how to open a biner on a saw laynard.
The Micky Mouse was the most difficult biner of all time for me to learn the feel for opening it. So I abandoned it. I still have it though and give it to people and ask them to open it. Some people need to be shown. And even after showing them it still takes them a minute to do.
To me a life-line connector should not be difficult to open and the fact that so many are gets me to wondering just how many accidents have resulted from it.
Rant over